Area sensor and display apparatus provided with an area sensor

ABSTRACT

An area sensor of the present invention has a function of displaying an image in a sensor portion by using light-emitting elements and a reading function using photoelectric conversion devices. Therefore, an image read in the sensor portion can be displayed thereon without separately providing an electronic display on the area sensor. Furthermore, a photoelectric conversion layer of a photodiode according to the present invention is made of an amorphous silicon film and an N-type semiconductor layer and a P-type semiconductor layer are made of a polycrystalline silicon film. The amorphous silicon film is formed to be thicker than the polycrystalline silicon film. As a result, the photodiode according to the present invention can receive more light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/145,863, filed May 4, 2016, now allowed, which is a continuation ofU.S. application Ser. No. 14/797,251, filed Jul. 13, 2015, now U.S. Pat.No. 9,337,243, which is a continuation of U.S. application Ser. No.13/760,121, filed Feb. 6, 2013, now U.S. Pat. No. 9,082,677, which is acontinuation of U.S. application Ser. No. 13/241,346, filed Sep. 23,2011, now U.S. Pat. No. 8,378,443, which is a continuation of U.S.application Ser. No. 12/754,702, filed Apr. 6, 2010, now U.S. Pat. No.8,058,699, which is a continuation of U.S. application Ser. No.11/278,841, filed Apr. 6, 2006, now U.S. Pat. No. 7,786,544, which is adivisional of U.S. application Ser. No. 09/924,108, filed Aug. 8, 2001,now U.S. Pat. No. 7,030,551, which claims the benefit of a foreignpriority application filed in Japan as Serial No. 2000-242932 on Aug.10, 2000, all of which are incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an area sensor (semiconductor device)having an image sensor function and a display function. In particular,the present invention relates to an area sensor (semiconductor device)that has EL (electroluminescence) elements as a light source and iscomposed of photoelectric conversion devices provided on a flat surface(insulating surface) and a plurality of thin film transistors (TFTs)arranged in a matrix.

2. Description of the Related Art

In recent years, a solid-state image sensing device is being used, whichhas diodes, CCDs, or the like for reading an electric signal havingimage information from a light signal having textural/graphicinformation, video information, and the like on a sheet of paper. Such asolid-state image sensing device is used for a scanner, a digitalcamera, and the like.

The solid-state image sensing device having photoelectric conversiondevices are classified into a line sensor and an area sensor. In theline sensor, photoelectric conversion devices provided in a line shapeare scanned with respect to a subject, whereby image information iscaptured as an electric signal.

The area sensor is also called a contact-type area sensor, in whichphotoelectric conversion devices provided on a flat surface are disposedon a subject, and image information is captured as an electric signal.Unlike the line sensor, it is not required to scan photoelectricconversion devices in the area sensor, so that a motor and the like forscanning are not necessary.

FIGS. 23A and 23B show a configuration of a conventional area sensor.FIG. 23A is a perspective view of the area sensor, and FIG. 23B is across-sectional view thereof. A sensor substrate 2501 with photoelectricconversion devices formed thereon, a backlight 2502, and a lightscattering plate 2503 are provided as shown in FIG. 23B.

Light from the backlight 2502 (light source) is refracted in the lightscattering plate 2503, and is radiated to a subject 2504. The radiatedlight is reflected from the subject 2504, and radiated to thephotoelectric conversion devices provided on the sensor substrate 2501.When the photoelectric conversion devices are irradiated with light, acurrent with a magnitude in accordance with the brightness of light isgenerated in the photoelectric conversion devices, and image informationof the subject 2504 is captured in the area sensor as an electricsignal.

In the above-mentioned area sensor, when light is not radiated uniformlyto the subject from the backlight 2502, a read image may partiallybecome light or dark, resulting in inconsistencies of the image. Thismakes it necessary to design the light scattering plate 2503 so thatlight is radiated uniformly to the subject 2504, and to precisely adjustthe position of the backlight 2502, the light scattering plate 2503, thesensor substrate 2501, and the subject 2504.

It is also difficult to minimize the size of the backlight 2502 and thelight scattering plate 2503, which prevents the area sensor frombecoming small, thin, and light-weight.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is an object of the presentinvention to provide an area sensor that is small, thin, andlight-weight, and in which a read image has no inconsistencies inlightness.

An area sensor of the present invention uses a photodiode as aphotoelectric conversion device. The area sensor also uses anelectroluminescense (EL) element as a light source.

In the present specification, a photodiode (photoelectric conversiondevice) includes an N-type semiconductor layer, a P-type semiconductorlayer, and a photoelectric conversion device provided so as to come intocontact with a part of the N-type semiconductor layer and the P-typesemiconductor layer.

When a photodiode is irradiated with light, the voltage thereof isdecreased due to carriers generated by the light. At this time, as lightintensity is higher, the amount of a decrease in voltage becomes larger.Furthermore, by comparing a voltage in the case where a photodiode isirradiated with light, with a voltage in the case where the photodiodeis not irradiated with light, a signal is input to a sensor signal line.

An EL element (light-emitting element) is a spontaneous light-emittingelement, and is mainly used for an EL display. An EL display is alsocalled an organic EL display (OELD) or an organic light-emitting diode(OLED).

An EL element has a configuration in which an EL layer (organic compoundlayer) is interposed between a pair of electrodes (positive electrodeand negative electrode), and the EL layer usually has a multi-layerconfiguration. Typically, there is a multi-layer configuration “holetransport layer/light-emitting layer/electron transport layer” proposedby Tang of Eastman Kodak. This configuration has a very highlight-emitting efficiency, and most of the EL display apparatuses thatare being studied and developed adopt this configuration.

Alternatively, an EL layer may have a configuration in which a holeinjection layer, a hole transport layer, a light-emitting layer, and anelectron transport layer are stacked in this order on an electrode or aconfiguration in which a hole injection layer, a hole transport layer, alight-emitting layer, an electron transport layer, and an electroninjection layer are stacked in this order on an electrode. Alight-emitting layer may be doped with a fluorescent colorant or thelike.

In the present specification, all the layers provided between a pair ofelectrodes are collectively referred to as an “EL layer (organiccompound layer)”. Therefore, the above-mentioned hole injection layer,hole transport layer, light-emitting layer, electron transport layer,electron injection layer, etc. are all included in the EL layer. Apredetermined voltage is applied to an EL layer with the above-mentionedconfiguration through a pair of electrodes, whereby carriers arerecombined in a light-emitting layer to emit light.

In the present specification, an EL element (light-emitting element) hasa configuration in which an organic compound layer is interposed betweena pair of electrodes (positive electrode and negative electrode). Theorganic compound layer can be made of a known light-emitting material.Furthermore, the organic compound layer can have a single-layerconfiguration and a multi-layer configuration. According to the presentinvention the organic compound layer may have either configuration. Asluminescence in the organic compound layer, there are light emission(fluorescence) occurring when a singlet excited state is changed to aground state and light emission (phosphorescence) occurring when atriplet excited state is changed to a ground state. According to thepresent invention, either light emission may be used.

Photodiodes and EL elements are provided on the same sensor substrate ina matrix. The photodiodes and the EL elements are controlled foroperation, respectively, using thin film transistors (TFTs) similarlyprovided on the substrate in a matrix.

Light emitted from the EL elements is reflected from a subject andradiated to the photodiodes. A current is generated by the lightradiated to the photodiodes, and an electric signal (image signal)having image information of the subject is captured by an area sensor.

According to the present invention, due to the above-mentionedconfiguration, light is radiated uniformly to a subject, so that noinconsistencies in lightness are caused in a read image. Furthermore, itis not required to provide a backlight and a light scattering plateseparately from a sensor substrate. Therefore, unlike a conventionalexample, an area sensor can be made small, thin, and light-weightwithout precisely adjusting the position of a backlight, a lightscattering plate, a sensor substrate, and a subject. Furthermore, themechanical strength of an area sensor is increased.

The area sensor of the present invention is also capable of displayingan image, using the EL elements. The EL elements in the presentinvention have a function as a light source for reading an image and afunction as a light source for displaying an image. Therefore, even whenan electronic display is not provided separately on the area sensor, animage can be displayed.

Examples of a film made of silicon include a single crystal siliconfilm, a polycrystalline silicon film (polysilicon film), an amorphoussilicon film (amorphous silicon film), etc. In the photodiode accordingto the present invention, a photoelectric conversion layer is made of anamorphous silicon film (amorphous silicon film), an N-type semiconductorlayer is made of an N-type polycrystalline silicon film (polysiliconfilm), and a P-type semiconductor layer is made of a polycrystallinesilicon film (polysilicon film). The amorphous silicon film is thickerthan the polycrystalline silicon film, and the ratio in thicknesstherebetween is preferably (1 to 10):1. In the photodiode used in thepresent invention, a photoelectric conversion layer can receive morelight when the thickness of the amorphous silicon film is larger thanthat of the polycrystalline silicon film.

According to the present invention, a photoelectric conversion layer ismade of an amorphous silicon film due to its high light absorptivity.

In a photodiode, a dark current (i.e., current flowing at a lightintensity of 0) may flow even when light is not radiated to thephotodiode. However, due to a high resistance of an amorphous siliconfilm, a current does not flow even under the condition of dark light,whereby a dark current can be decreased. More specifically, when a darkcurrent is small, a range of lightness and darkness of light which aphotodiode can receive is enlarged in the case of dark light.

As shown in FIG. 16, a metal film 280 can also be formed so as to covera first interlayer insulating film 250 provided on a photoelectricconversion layer 248.

Light is radiated to a subject 270 from an EL element, and lightreflected form the subject 270 is radiated to a photodiode 306. However,in this case, among light passing through the photodiode 306, thereexists light that is not radiated to the photoelectric conversion layer248. If the metal film 280 is present as shown in FIG. 16, such light isreflected from the metal film 280, whereby the photoelectric conversionlayer 248 can receive it. Because of this, the photoelectric conversionlayer 248 can receive more light.

Hereinafter, the constitution of the present invention will bedescribed.

According to the present invention, there is provided an area sensor,characterized in that:

the sensor comprises a sensor portion provided with a plurality ofpixels each including a photodiode, an EL element, and a plurality ofthin film transistors;

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

According to the present invention, there is provided an area sensor,characterized in that:

the sensor comprises a sensor portion provided with a plurality ofpixels each including a photodiode, an EL element, and a plurality ofthin film transistors;

the pixel includes a photodiode, an EL element, a switching TFT, an ELdriving TFT, a reset TFT, a buffer TFT, and a selective TFT;

the switching TFT and the EL driving TFT control light emission of theEL element; light emitted from the EL element is reflected from asubject to be radiated to the photodiode;

the photodiode, the reset TFT, the buffer TFT, and the selective TFTgenerate an image signal from the light radiated to the photodiode;

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

According to the present invention, there is provided an area sensor,characterized in that:

the area sensor comprises a sensor portion provided with a plurality ofpixels each including a photodiode, an EL element, and a plurality ofthin film transistors;

the pixel includes a photodiode, an EL element, a switching TFT, an ELdriving TFT, a reset TFT, a buffer TFT, a selective TFT, a source signalline, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

a gate electrode of the switching TFT is connected to the gate signalline;

one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

a source region of the EL driving TFT is connected to the power supplyline, and a drain region of the EL driving TFT is connected to the ELelement;

a source region of the reset TFT is connected to the sensor power sourceline;

a drain region of the reset TFT is connected to a gate electrode of thebuffer TFT and the photodiode;

a drain region of the buffer TFT is connected to the sensor power sourceline;

one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

a gate electrode of the selective TFT is connected to the sensor gatesignal line,

light emitted from the EL element is reflected from a subject to beradiated to the photodiode,

an image signal generated from the light radiated to the photodiode isinput to the sensor output line,

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film, and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

According to the present invention, there is provided an area sensor,characterized in that:

the area sensor comprises a sensor portion provided with a plurality ofpixels each including a photodiode, an EL element, and a plurality ofthin film transistors;

the pixel includes a photodiode, an EL element, a switching TFT, an ELdriving TFT, a reset TFT, a buffer TFT, a selective TFT, a source signalline, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

a gate electrode of the switching TFT is connected to the gate signalline;

one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

a source region of the EL driving TFT is connected to the power supplyline, and a drain region of the EL driving TFT is connected to the ELelement;

a source region of the reset TFT is connected to the sensor power sourceline;

a drain region of the reset TFT is connected to a gate electrode of thebuffer TFT and the photodiode;

a drain region of the buffer TFT is connected to the sensor power sourceline;

one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

a gate electrode of the selective TFT is connected to the sensor gatesignal line;

a polarity of the switching TFT is the same as that of the selectiveTFT;

light emitted from the EL element is reflected from a subject to beradiated to the photodiode;

an image signal generated from the light radiated to the photodiode isinput to the sensor output line;

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

According to the present invention, there is provided an area sensor,characterized in that:

the area sensor comprises a sensor portion provided with a plurality ofpixels each including a photodiode, an EL element, and a plurality ofthin film transistors;

the pixel includes a photodiode, an EL element, a switching TFT, an ELdriving TFT, a reset TFT, a buffer TFT, a selective TFT, a source signalline, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

a gate electrode of the switching TFT is connected to the gate signalline;

one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

a source region of the EL driving TFT is connected to the power supplyline, and a drain region of the EL driving TFT is connected to the ELelement;

a source region of the reset TFT is connected to the sensor power sourceline;

a drain region of the reset TFT is connected to a gate electrode of thebuffer TFT and the photodiode;

a drain region of the buffer TFT is connected to the sensor power sourceline;

one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

a gate electrode of the selective TFT is connected to the sensor gatesignal line;

the reset TFT and the selective TFT are switched from an ON state to anOFF state or from an OFF state to an ON state by a signal input to thereset gate signal line and the sensor gate signal line;

when one of the reset TFT and the selective TFT is in an ON state, theother is in an OFF state;

light emitted from the EL element is reflected from a subject to beradiated to the photodiode;

an image signal generated from the light radiated to the photodiode isinput to the sensor output line;

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

According to the present invention, there is provided an area sensor,characterized in that:

the area sensor comprises a sensor portion provided with a plurality ofpixels each including a photodiode, an EL element, and a plurality ofthin film transistors;

the pixel includes a photodiode, an EL element, a switching TFT, an ELdriving TFT, a reset TFT, a buffer TFT, a selective TFT, a source signalline, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

a gate electrode of the switching TFT is connected to the gate signalline;

one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

a source region of the EL driving TFT is connected to the power supplyline, and a drain region of the EL driving TFT is connected to the ELelement;

a source region of the reset TFT is connected to the sensor power sourceline;

a drain region of the reset TFT is connected to a gate electrode of thebuffer TFT and the photodiode;

a drain region of the buffer TFT is connected to the sensor power sourceline;

one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

a gate electrode of the selective TFT is connected to the sensor gatesignal line;

a polarity of the switching TFT is the same as that of the selectiveTFT;

the reset TFT and the selective TFT are switched from an ON state to anOFF state or from an OFF state to an ON state by a signal input to thereset gate signal line and the sensor gate signal line;

when one of the reset TFT and the selective TFT is in an ON state, theother is in an OFF state;

light emitted from the EL element is reflected from a subject to beradiated to the photodiode;

an image signal generated from the light radiated to the photodiode isinput to the sensor output line;

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

According to the present invention, there is provided a display device,characterized in that:

the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer and is made of an amorphous semiconductor film; and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

According to the present invention, there is provided a display device,characterized in that:

the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

the pixel includes a photodiode, an EL element, a switching TFT, an ELdriving TFT, a reset TFT, a buffer TFT, and a selective TFT;

the switching TFT and the EL driving TFT controls light emission of theEL element; light emitted from the EL element is reflected from asubject to be radiated to the photodiode;

the photodiode, the reset TFT, the buffer TFT, and the selective TFTgenerate an image signal from the light radiated to the photodiode;

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer and is made of an amorphous semiconductor film; and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

According to the present invention, there is provided a display device,characterized in that:

the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

the pixel includes a photodiode, an EL element, a switching TFT, an ELdriving TFT, a reset TFT, a buffer TFT, a selective TFT, a source signalline, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

a gate electrode of the switching TFT is connected to the gate signalline;

one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

a source region of the EL driving TFT is connected to the power supplyline, and a drain region of the EL driving TFT is connected to the ELelement;

a source region of the reset TFT is connected to the sensor power sourceline;

a drain region of the reset TFT is connected to a gate electrode of thebuffer TFT and the photodiode;

a drain region of the buffer TFT is connected to the sensor power sourceline;

one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

a gate electrode of the selective TFT is connected to the sensor gatesignal line;

light emitted from the EL element is reflected from a subject to beradiated to the photodiode;

an image signal generated from the light radiated to the photodiode isinput to the sensor output line;

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

According to the present invention, there is provided a display device,characterized in that:

the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

the pixel includes a photodiode, an EL element, a switching TFT, an ELdriving TFT, a reset TFT, a buffer TFT, a selective TFT, a source signalline, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

a gate electrode of the switching TFT is connected to the gate signalline;

one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

a source region of the EL driving TFT is connected to the power supplyline, and a drain region of the EL driving TFT is connected to the ELelement;

a source region of the reset TFT is connected to the sensor power sourceline;

a drain region of the reset TFT is connected to a gate electrode of thebuffer TFT and the photodiode;

a drain region of the buffer TFT is connected to the sensor power sourceline;

one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

a gate electrode of the selective TFT is connected to the sensor gatesignal line;

a polarity of the switching TFT is the same as that of the selectiveTFT;

light emitted from the EL element is reflected from a subject to beradiated to the photodiode;

an image signal generated from the light radiated to the photodiode isinput to the sensor output line;

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

According to the present invention, there is provided a display device,characterized in that:

the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

the pixel includes a photodiode, an EL element, a switching TFT, an ELdriving TFT, a reset TFT, a buffer TFT, a selective TFT, a source signalline, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

a gate electrode of the switching TFT is connected to the gate signalline;

one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

a source region of the EL driving TFT is connected to the power supplyline, and a drain region of the EL driving TFT is connected to the ELelement;

a source region of the reset TFT is connected to the sensor power sourceline;

a drain region of the reset TFT is connected to a gate electrode of thebuffer TFT and the photodiode;

a drain region of the buffer TFT is connected to the sensor power sourceline;

one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

a gate electrode of the selective TFT is connected to the sensor gatesignal line;

the reset TFT and the selective TFT are switched from an ON state to anOFF state or from an OFF state to an ON state by a signal input to thereset gate signal line and the sensor gate signal line;

when one of the reset TFT and the selective TFT is in an ON state, theother is in an OFF state;

light emitted from the EL element is reflected from a subject to beradiated to the photodiode;

an image signal generated from the light radiated to the photodiode isinput to the sensor output line;

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

According to the present invention, there is provided a display device,characterized in that:

the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

the pixel includes a photodiode, an EL element, a switching TFT, an ELdriving TFT, a reset TFT, a buffer TFT, a selective TFT, a source signalline, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

a gate electrode of the switching TFT is connected to the gate signalline;

one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

a source region of the EL driving TFT is connected to the power supplyline, and a drain region of the EL driving TFT is connected to the ELelement;

a source region of the reset TFT is connected to the sensor power sourceline;

a drain region of the reset TFT is connected to a gate electrode of thebuffer TFT and the photodiode;

a drain region of the buffer TFT is connected to the sensor power sourceline;

one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

a gate electrode of the selective TFT is connected to the sensor gatesignal line;

a polarity of the switching TFT is the same as that of the selectiveTFT;

the reset TFT and the selective TFT are switched from an ON state to anOFF state or from an OFF state to an ON state by a signal input to thereset gate signal line and the sensor gate signal line;

when one of the reset TFT and the selective TFT is in an ON state, theother is in an OFF state;

light emitted from the EL element is reflected from a subject to beradiated to the photodiode;

an image signal generated from the light radiated to the photodiode isinput to the sensor output line;

the photodiode includes a photoelectric conversion layer that is incontact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a circuit diagram of a sensor portion;

FIG. 2 is a circuit diagram of a pixel;

FIG. 3 is a timing chart of reading of an image in the sensor portion;

FIG. 4 is a timing chart of reading of a color image in the sensorportion;

FIG. 5 is a top view of an area sensor for digital driving;

FIG. 6 is a timing chart of light emission of an EL element when animage is read;

FIG. 7 is a timing chart of light emission of an EL element when animage is displayed;

FIG. 8 is a top view of an area sensor for analog driving;

FIG. 9 is a timing chart of light emission of an EL element when animage is read;

FIGS. 10A to 10C show the steps of producing the sensor portion;

FIGS. 11A to 11C show the steps of producing the sensor portion;

FIGS. 12A to 12C show the steps of producing the sensor portion;

FIGS. 13A to 13C show the steps of producing the sensor portion;

FIGS. 14A and 14B show the steps of producing the sensor portion;

FIG. 15 is an enlarged view of a photodiode according to the presentinvention;

FIG. 16 is an enlarged view of a photodiode according to the presentinvention;

FIGS. 17A and 17B are top views of the sensor portion of an area sensorof the present invention;

FIGS. 18A to 18C show a schematic view and cross-sectional views of thesensor portion of the area sensor of the present invention;

FIGS. 19A to 19C show the production steps according to the presentinvention;

FIGS. 20A and 20B show the production steps according to the presentinvention;

FIGS. 21A and 21B show an outer appearance of a portable hand scannerthat is an exemplary area sensor of the present invention;

FIG. 22 shows an outer appearance of an area sensor provided with atouch panel that is an exemplary area sensor of the present invention;

FIGS. 23A and 23B are a perspective view and a cross-sectional view of aconventional area sensor;

FIG. 24 is a circuit diagram of a sensor portion; and

FIGS. 25A to 25C show exemplary electronic equipment to which thepresent invention is applicable.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the structure of an area sensor (semiconductor device) ofthe present invention will be described. The area sensor of the presentinvention includes a sensor portion for reading an image and a drivingportion for controlling driving of the sensor portion. FIG. 1 shows acircuit diagram of the sensor portion according to the presentinvention.

A sensor portion 101 is provided with source signal lines S₁ to S_(x),power supply lines V₁ to V_(x), gate signal lines G₁ to G_(y), resetgate signal lines RG₁ to RG_(y), sensor gate signal lines SG₁ to SG_(y),sensor output lines SS₁ to SS_(x), and a sensor power source line VB.

The sensor portion 101 has a plurality of pixels 102. Each pixel 102includes one of the source signal lines S₁ to S_(x), one of the powersupply lines V₁ to V_(x), one of the gate signal lines G₁ to G_(y), oneof reset the gate signal lines RG₁ to RG_(y), one of the sensor gatesignal lines SG₁ to SG_(y), one of the sensor output lines SS₁ toSS_(x), and the sensor power source line VB.

The sensor output lines SS₁ to SS_(x) are respectively connected toconstant current power sources 103_ ₁ to 103_ _(x) .

FIG. 2 shows a detailed configuration of the pixel 102. A regionsurrounded by a dotted line is the pixel 102. A source signal line Sdenotes one of the source signal lines S₁ to S_(x). A power supply lineV denotes one of the power supply lines V₁ to V_(x). A gate signal lineG denotes one of the gate signal lines G₁ to G_(y). A reset gate signalline RG denotes one of the reset gate signal lines RG₁ to RG_(y). Asensor gate signal line SG denotes one of the sensor gate signal linesSG₁ to SG_(y). A sensor output line SS denotes one of sensor outputlines SS₁ to SS_(x).

The pixel 102 includes a switching TFT 104, an EL driving TFT 105, andan EL element 106. In FIG. 2, although a capacitor 107 is provided inthe pixel 102, the capacitor 107 may not be provided.

The EL element 106 is composed of a positive electrode, a negativeelectrode, and an EL layer provided between the positive electrode andthe negative electrode. In the case where the positive electrode isconnected to a source region or a drain region of the EL driving TFT105, the positive electrode functions as a pixel electrode and thenegative electrode functions as a counter electrode. In contrast, in thecase where the negative electrode is connected to a source region or adrain region of the EL driving TFT 105, the positive electrode functionsas a counter electrode and the negative electrode functions as a pixelelectrode.

A gate electrode of the switching TFT 104 is connected to the gatesignal line G. One of a source region and a drain region of theswitching TFT 104 is connected to the source signal line S, and theother is connected to the gate electrode of the EL driving TFT 105.

The source region of the EL driving TFT 105 is connected to the powersupply line V, and the drain region of the EL driving TFT 105 isconnected to the EL element 106. The capacitor 107 is provided so as tobe connected to the gate electrode of the EL driving TFT 105 and thepower supply line V.

The pixel 102 further includes a reset TFT 110, a buffer TFT 111, aselective TFT 112, and a photodiode 113.

A gate electrode of the reset TFT 110 is connected to the reset gatesignal line RG. A source region of the reset TFT 110 is connected to thesensor power source line VB. The sensor power source line VB is alwayskept at a constant electric potential (reference potential). A drainregion of the reset TFT 110 is connected to the photodiode 113 and agate electrode of the buffer TFT 111.

Although not shown in the figure, the photodiode 113 has an N-typesemiconductor layer, a P-type semiconductor layer, and a photoelectricconversion layer provided between the N-type semiconductor layer and theP-type semiconductor layer. The drain region of the reset TFT 110 isconnected to either the P-type semiconductor layer or the N-typesemiconductor layer of the photodiode 113.

A drain region of the buffer TFT 111 is connected to the sensor powersource line VB, and is always kept at a constant reference potential. Asource region of the buffer TFT 111 is connected to a source region or adrain region of the selective TFT 112.

A gate electrode of the selective TFT 112 is connected to the sensorgate signal line SG. One of a source region and a drain region of theselective TFT 112 is connected to the source region of the buffer TFT111 as described above, and the other is connected to the sensor outputline SS. The sensor output line SS is connected to the constant currentpower source 103 (one of the constant current power sources 103_ ₁ to103_ _(x) ), and is always supplied with a constant current.

Hereinafter, a method for driving the area sensor of the presentinvention will be briefly described with reference to FIGS. 1 and 2.

The EL element 106 of the pixel 102 functions as a light source of thearea sensor, and the switching TFT 104, the EL driving TFT 105, and thecapacitor 107 control the operation of the EL element 106 as a lightsource.

Light emitted from the EL element 106 is reflected from a subject, andradiated to the photodiode 113 of the pixel 102. The photodiode 113transforms the radiated light into an electric signal having imageinformation. The electric signal having image information generated inthe photodiode 113 is captured in the area sensor as an image signal bythe reset TFT 110, the buffer TFT 111, and the selective TFT 112.

FIG. 3 is a timing chart showing the operation of the reset TFT 110, thebuffer TFT 111, and the selective TFT 112. FIG. 3 shows a timing chartin which the reset TFT 110 is an N-channel type TFT, the buffer TFT 111is a P-channel type TFT, and the selective TFT 112 is an N-channel typeTFT. According to the present invention, the reset TFT 110, the bufferTFT 111, and the selective TFT 112 may be an N-channel type TFT or aP-channel type TFT. It is preferable that the polarity of the reset TFT110 is opposite to that of the buffer TFT 111.

First, the reset TFTs 110 for pixels in the first line, connected to thereset gate signal Line RG₁, are turned on with a reset signal input tothe reset gate signal line RG₁. Then, the reference potential of thesensor power source line VB is given to the gate electrodes of thebuffer TFTs 111.

The selective TFTs 112 for the pixels in the first line, connected tothe sensor gate signal line SG₁ are turned off with a sensor signalinput to the sensor gate signal line SG₁. Thus, the source region ofeach buffer TFT 111 is kept at an electric potential obtained bysubtracting a potential difference V_(GS) between the source region andthe gate region of the buffer TFT 111 from the reference potential. Inthe present specification, a period during which the reset TFTs 110 arein an ON state is referred to as a reset period.

Then, the electric potential of the reset signal input to the reset gatesignal line RG₁ is changed, whereby all of the reset TFTs 110 for thepixels in the first line are turned off. As a result, the referencepotential of the sensor power source line VB is not given to each gateelectrode of the buffer TFTs 111 for the pixels in the first line. Inthe present specification, a period during which the reset TFTs 110 arein an OFF state is referred to as a sampling period ST. In particular, aperiod during which the reset TFTs 110 for the pixels in the first lineare in an OFF state is referred to as a sampling period ST₁

During the sampling period ST₁, the electric potential of the sensorsignal input to the sensor gate signal line SG₁ is changed, and theselective TFTs 112 for the pixels in the first line are turned on. Thus,the source regions of the buffer TFTs 111 for the pixels in the firstline are electrically connected to the sensor output line SS₁ via theselective TFTs 112. The sensor output line SS₁ is connected to theconstant current power sources 103_ ₁ . Therefore, each buffer TFT 111functions as a source follower, whereby the potential difference V_(GS)between the source region and the gate region of the buffer TFT 111becomes constant.

When light emitted from the EL elements 106 is reflected from a subjectand radiated to the photodiodes 113 during the sampling period ST₁, acurrent flows through the photodiodes 113. Therefore, the electricpotential of the gate electrodes of the buffer TFTs 111 kept at thereference potential during the reset period is increased in accordancewith the magnitude of a current generated in the photodiodes 113.

A current flowing through each photodiode 113 is proportional to theintensity of light radiated to the photodiode 113. Therefore, imageinformation of the subject is transformed to an electric signal as it isby the photodiode 113. The electric signal generated in the photodiode113 is input to the gate electrode of the buffer TFT 111.

The potential different V_(GS) between the source region and the gateregion of the buffer TFT 111 is always kept constant. Therefore, thesource region of the buffer TFT 111 is kept at an electric potentialobtained by subtracting the potential difference V_(GS) from theelectric potential of the gate electrode of the buffer TFT 111.Consequently, when the electric potential of the gate electrode of thebuffer TFT 111 is changed, the electric potential of the source regionof the buffer TFT 111 is also changed in accordance therewith.

The electric potential of the source region of the buffer TFT 111 isinput of the sensor output line SS₁ via the selective TFT 112 as animage signal.

Next, the reset TFTs 110 for the pixels in the first line, connected tothe reset gate signal line RG₁, are turned on with a reset signal inputto the reset gate signal line RG₁, and a reset period is obtained again.Simultaneously, the reset TFTs 110 for pixels in the second line,connected to the reset gate signal line RG 2, are turned off with areset signal input to the reset gate signal line RG₂, whereby a samplingperiod ST₂ starts.

During the sampling period ST₂, in the same way as in the samplingperiod ST₁, an electric signal having image information is generated inthe photodiodes, and an image signal is input to the sensor output lineSS₂.

When the above-mentioned operation is repeated, and the sampling periodST_(y) is completed, one image can be read as an image signal. In thepresent specification, a period during which all the sampling periodsST₁ to ST_(y) are completed is referred to as a sensor frame period SF.

During each sampling period, it is required to allow the EL element ofeach pixel to emit light. For example, it is important that the ELelements of the pixels in the first line emit light during at least thesampling period ST₁. All the pixels may emit light during the sensorframe period SF.

In the case of an area sensor for reading a color image, a sensorportion has pixels corresponding to red (R), green (G), and blue (B)colors. Pixels corresponding to RGB colors have three kinds of ELelements corresponding to RGB colors. Alternatively, they have an ELelement for emitting white light and three kinds of RGB color filters.Alternatively they have an EL element for emitting blue light orblue-green light and a phosphor (fluorescent color transforming layer:CCM).

Light with RGB colors emitted from the pixels corresponding to RGBcolors is radiated to a subject successively. Light of each of RGBcolors reflected from the subject is radiated to photodiodes of thepixels, and image signals corresponding to RGB colors are captured inthe area sensor.

FIG. 4 shows a timing chart showing the operation of the reset TFT 110,the buffer TFT 111, and the selective TFT 112 of the area sensor forreading a color image. FIG. 4 shows a timing chart in which the resetTFT 110 is an N-channel type TFT, the buffer TFT 111 is a P-channel typeTFT, and the selective TFT 112 is an N-channel type TFT.

While EL elements of pixels corresponding to R emit light, all thesampling periods ST₁ to ST_(y) appear. A period during which all thesampling periods ST₁ to ST_(y) are completed during a period in whichthe EL elements of the pixels corresponding to R emit light is referredto as an R sensor frame period SF_(r). During the R sensor frame periodSF_(r), an image signal corresponding to R is captured in the areasensor. During the R sensor frame SF_(r), pixels corresponding to G andB do not emit light.

Next, while EL elements of the pixels corresponding to G emit light, allthe sampling periods TS₁ to ST_(y) appear. A period during which all thesampling periods ST₁ to ST_(y) are completed during a period in whichthe EL elements of the pixels corresponding to G emit light is referredto as a G sensor frame period SF_(g). During the G sensor frame periodSF_(g), an image signal corresponding to G is captured in the areasensor. During the G sensor frame SF_(g), pixels corresponding to R andB do not emit light.

Next, while EL elements of the pixels corresponding to B emit light, allthe sampling periods TS₁ to ST_(y) appear. A period during which all thesampling periods ST₁ to ST_(y) are completed during a period in whichthe EL elements of the pixels corresponding to B emit light is referredto as a B sensor frame period SF_(b). During the B sensor frame periodSF_(b), an image signal corresponding to B is captured in the areasensor. During the B sensor frame SF_(b), pixels corresponding to R andG do not emit light.

A period during which all the R sensor frame period SF_(r), the G sensorframe period SF_(g), and the B sensor frame period SF_(b) are completedis a sensor frame period SF. When the sensor frame period SF iscompleted, one color image can be read as an image signal.

Furthermore, during each sampling period, it is required to allow the ELelements of the pixels corresponding to each color to always emit light.For example, during the sampling period ST₁ in the B sensor frameperiod, it is important that the EL elements of the pixels correspondingto B among those in the first line always emit light. Pixelscorresponding to each color may always emit light during each of the R,G, and B sensor frame period (SF_(r), SF_(g), SF_(b)).

According to the present invention, due to the above-mentionedconstitution, light is radiated uniformly to a subject. Therefore,inconsistencies are not caused in lightness of a read image. It is notrequired to provide a backlight and a light scattering plate separatelyfrom a sensor substrate (i.e., substrate having an insulating surface onwhich EL elements and photoelectric conversion devices are provided).Therefore, unlike the conventional example, an area sensor itself can bemade small, thin, and light-weight without precisely adjusting theposition of the backlight, the light scattering plate, the sensorsubstrate, and the subject. The mechanical strength of the area sensoritself is also increased.

Furthermore, the area sensor of the present invention is capable ofdisplaying an image in a sensor portion, using EL elements (lightsource). Therefore, an image read by photodiodes can be displayed in thesensor portion without separately providing an electronic display on anarea sensor, and a read image can be confirmed as soon as it is read.

EMBODIMENTS

Hereinafter, the present invention will be described by way ofillustrative embodiments with reference to the drawings.

Embodiment 1

A method of driving the switching TFT 104 and the EL driving TFT 105,which control the operation of the EL element 106 shown in FIG. 2, isexplained in Embodiment 1. Note that the structure of the sensor portionis the same as that of the embodiment mode, and therefore FIG. 1 andFIG. 2 are referenced.

FIG. 5 shows a top view of an area sensor of Embodiment 1. Referencenumeral 120 denotes a source signal line driving circuit, referencenumeral 122 denotes a gate signal line driving circuit, and both controlthe driving of the switching TFT 104 and the EL driving TFT 105.Further, reference numeral 121 denotes a sensor source signal linedriving circuit, reference numeral 123 denotes a sensor gate signal linedriving circuit, and both control the driving of the reset TFT 110, thebuffer TFT 111, and the selection TFT 112. Note that the source signalline driving circuit 120, the gate signal line driving circuit 122, thesensor source signal line driving circuit 121, and the sensor gatesignal line driving circuit 123 are referred to as a driving portion.

The source signal line driving circuit 120 has a shift register 120 a, alatch (A) 120 b, and a latch (B) 120 c. A clock signal (CLK) and a startpulse (SP) are inputted to the shift register 120 a in the source signalline driving circuit 120. The shift register 120 a generates timingsignals in order based upon the clock signal (CLK) and the start pulse(SP), and the timing signals are supplied one after another todownstream circuits.

Note that the timing signals from the shift register 120 a may bebuffer-amplified by a circuit such as a buffer (not shown in the figure)and then supplied one after another to the downstream circuits as thebuffer-amplified timing signals. The load capacitance (parasiticcapacitance) of a wiring to which the timing signals are supplied islarge because many of the circuits and elements are connected to thewiring. The buffer is formed in order to prevent dullness in the riseand fall of the timing signal, generated due to the large loadcapacitance.

The timing signals from the shift register 120 a are supplied to thelatch (A) 120 b. The latch (A) 120 b has a plurality of latch stages forprocessing a digital signal. The latch (A) 120 b writes in and maintainsdigital signals in order simultaneously with the input of the timingsignals.

Note that the digital signals may be sequentially inputted to theplurality of latch stages of the latch (A) 120 b when the digitalsignals are taken in by the latch (A) 120 b. However, the presentinvention is not limited to this structure. A so-called division drivemay be performed, that is, the plurality of latch stages of the latch(A) 120 b is divided into a number of groups, and then the digitalsignals are parallel inputted to the respective groups at the same time.Note that the number of groups at this point is called a divisionnumber. For example, if the latch circuits are grouped into 4 stageseach, then it is called a 4-branch division drive.

The time necessary to complete writing of the digital signals into allthe latch stages of the latch (A) 120 b is called a line period. Inother words, the line period is defined as a time interval from thestart of writing the digital data signals into the latch circuit of theleftmost stage to the end of writing the digital signals into the latchof the rightmost stage in the latch (A) 120 b. In effect, theabove-defined line period added with the horizontal retrace period mayalso be referred to as the line period.

After the completion of one line period, a latch signal is supplied tothe latch (B) 120 c. In this moment, the digital signals written in andheld by the latch (A) 120 b are sent all at once to the latch (B) 120 cto be written in and held by all the latch stages thereof.

Sequential writing-in of digital signals on the basis of the timingsignals from the shift register 120 a is again carried out to the latch(A) 120 b after it has completed sending the digital signals to thelatch (B) 120 c.

During this second time one line period, the digital signals written inand held by the latch (B) 120 c are inputted to the source signal linesS1 to Sx.

On the other hand, the gate signal line driving circuit 122 is composedof a shift register and a buffer (both not shown in the figure).Depending on the situation, the gate signal line driving circuit 122 mayhave a level shifter in addition to the shift register and the buffer.

In the gate signal line driving circuit 122, the gate signal is suppliedto the buffer (not shown in the figure) from the shift register (alsonot shown in the figure), and this is supplied to a corresponding gatesignal line. Gate electrodes of the switching TFTs 104 of one lineportion of pixels are connected to each of the gate signal lines G1 toGy. All of the switching TFTs 104 of the one line portion of pixels mustbe placed in an ON state simultaneously, and therefore a buffer in whicha large electric current can flow is used.

Note that the number of source signal line driving circuits and gatesignal line driving circuits, their structure, and their operation arenot limited to the structure shown by Embodiment 1. The area sensor ofthe present invention is capable of using a known source signal linedriving circuit and a known gate signal line driving circuit.

Next, a timing chart for a case of driving the switching TFT 104 and theEL driving TFT 105 of the sensor portion by a digital method is shown inFIG. 6.

A period through which all of the pixels of the sensor portion 101 emitlight is referred to as one frame period F. The frame period is dividedinto an address period Ta and a sustain period Ts. The address period isa period in which a digital signal is inputted to all of the pixelsduring one frame period. The sustain period (also referred to as aturn-on period) denotes a period in which the EL elements emit light ornot in accordance with the digital signal inputted to the pixels in theaddress period and display is performed.

The electric potential of the electric power source supply lines V1 toVx is maintained at a predetermined electric potential (electric powersource potential).

First, in the address period Ta, the electric potential of the opposingelectrode of the EL element 106 is maintained at the same height as theelectric power source potential.

Then all of the switching TFTs 104 connected to the gate signal line G1turn on in accordance with a gate signal inputted to the gate signalline G1. A digital signal is next inputted from the source signal linedriving circuit 120 to the source signal lines S1 to Sx. The digitalsignal inputted to the source signal lines S1 to Sx is inputted to thegate electrodes of the EL driving TFTs 105 through the switching TFTs104 which are in an ON state.

Next, all of the switching TFTs 104 connected to the gate signal line G2are placed in an ON state in accordance with a gate signal inputted tothe gate signal line G2. The digital signal is then inputted from thesource signal line driving circuit 120 to the source signal lines S1 toSx. The digital signal inputted to the source signal lines S1 to Sx isinputted to the gate electrodes of the EL driving TFTs 105 through theswitching TFTs 104 which are in an ON state.

The above operations are repeated through the gate signal line Gy, thedigital signal is inputted to the gate electrodes of the EL driving TFTs105 of all the pixels 102, and the address period is completed.

The sustain period begins simultaneously to the end of the addressperiod Ta. All of the switching TFTs 104 are placed in an OFF state inthe sustain period.

Then, at the same time as the sustain period begins, the electricpotential of the opposing electrodes of all the EL elements has a heightof the electric potential difference between the electric power sourcepotential to the level at which the EL elements will emit light when theelectric potential of the electric power source is applied to the pixelelectrodes. Note that the electric potential difference between thepixel electrode and the opposing electrode is referred to as an ELdriving voltage in this specification. Further, the EL driving TFTs 105are placed in an ON state in accordance with the digital signal inputtedto the gate electrode of the EL driving TFTs 105 of each pixel.Therefore, the electric power source potential is applied to the pixelelectrodes of the EL elements, and the EL elements of all pixels emitlight.

One frame period is completed at the same time as the sustain period iscompleted. It is necessary that the pixels emit light in all of thesampling periods ST1 to STy with the present invention. Therefore, it isvery important that the sensor frame period SF be included within thesustain period when using the digital driving method of Embodiment 1.

Note that an explanation of a method of driving the area sensor forreading in a single color image is explained in Embodiment 1, but a caseof reading in a color image is similar. However, for the case of an areasensor which reads in a color image, one frame period is divided intothree subframe periods corresponding to RGB, and an address period and asustain period are formed in each subframe period. A digital signal isinputted to all of the pixels such that only the EL elements of pixelscorresponding to R will emit light, and only the EL elements for thecolor R perform light emission in the sustain period. The subframeperiods for G and B are similar, and only EL elements of pixelscorresponding to the respective colors perform light emission in eachsustain period.

For the case of an area sensor which reads in a color image, it isimportant that each sustain period of the three subframe periodscorresponding to RGB contains a sensor frame period for R, G, and B(SFr, SFg, SFb), respectively.

Embodiment 2

A method of driving the switching TFT 104 and the EL driving TFT 105when displaying an image in the sensor portion 101 is explained inEmbodiment 2. Note that the structure of the sensor portion is the sameas the structure shown by the embodiment mode, and therefore FIG. 1 andFIG. 2 may be referenced.

A timing chart when performing display of an image in the sensor portion101 in the area sensor of the present invention by a digital method isshown in FIG. 7.

First, one frame period F is divided into N subframe periods SF1 to SFN.The number of subframe periods in one frame period also increases as thenumber of gray scales increases. Note that, when the sensor portion ofthe area sensor displays an image, one frame period F denotes a periodduring which all pixels of the sensor portion display one image.

It is preferable that 60 or more frame periods be provided each secondfor the case of Embodiment 2. By setting the number of images displayedeach second to 60 or greater, it becomes possible to visually suppressimage flicker.

The subframe period is divided into an address period Ta and a sustainperiod Ts. The address period is a period within one subframe periodduring which a digital video signal is inputted to all pixels. Note thatthe digital video signal is a digital signal having image information.The sustain period (also referred to as a turn-on period) denotes aperiod during which EL elements are placed in a state of emitting lightor not emitting light in accordance with the digital video signalinputted to the pixels in the address period and display is performed.Note that the digital video signal denotes the digital signal havingimage information.

The address periods Ta of SF1 to SFN are taken as address periods Ta1 toTaN, and the sustain periods Ts of SF1 to SFN are taken as sustainperiods Ts1 to TsN.

The electric potential of the electric power source supply lines V1 toVx is maintained at a predetermined electric potential (electric powersource potential).

First, the electric potential of the opposing electrode of the ELelements 106 is maintained at the same height as the electric powersource potential in the address period Ta.

Next, all of the switching TFTs 104 connected to the gate signal line G1are placed in an ON state in accordance with a gate signal inputted tothe gate signal line G1. The digital video signal is then inputted tothe source signal lines S1 to Sx from the source signal line drivingcircuit 102. The digital video signal has “0” or “1” information, andone of the “0” and “1” digital video signals is a signal having a “HI”voltage, while the other is a signal having a “LO” voltage.

The digital video signal inputted to the source signal lines S1 to Sx isthen inputted to the gate electrodes of the EL driving TFTs 105 throughthe switching TFTs 104 in an ON state.

All of the switching TFTs 104 connected to the gate signal line G1 arethen placed in an OFF state, and all of the switching TFTs 104 connectedto the gate signal line G2 are placed in an ON state in accordance witha gate signal inputted to the gate signal line G2. The digital videosignal is then inputted to the source signal lines S1 to Sx from thesource signal line driving circuit 102. The digital video signalinputted to the source signal lines S1 to Sx is inputted to the gateelectrodes of the EL driving TFTs 105 through the switching TFTs 104 inan ON state.

The above operations are repeated through the gate signal line Gy, andthe digital video signal is inputted to the gate electrodes of the ELdriving TFTs 105 of all the pixels 102, and the address period iscompleted.

The sustain period Ts begins simultaneously with the completion of theaddress period Ta. All of the switching TFTs 104 are in an OFF state inthe sustain period. The electric potential of the opposing electrodes ofall the EL elements has a height of the electric potential differencebetween the electric power source potential to the level at which the ELelements will emit light when the electric potential of the electricpower source is applied to the pixel electrodes.

When the digital video signal has “0” information, the EL driving TFT105 is placed in an OFF state in Embodiment 2. The pixel electrode ofthe EL elements is therefore maintained at the electric potential of theopposing electrode. As a result, the EL element 106 does not emit lightwhen the digital video signal having “0” information is inputted to thepixel.

On the other hand, when the digital video signal has “1” information,the EL driving TFTs 105 are placed in an ON state. The electric powersource potential is therefore applied to the pixel electrode of the ELelement 106. As a result, the EL element 106 of the pixel into which thedigital video signal having “1” information is inputted emits light.

The EL elements are thus placed in a state in which they emit light ordo not emit light in accordance with the information of the digitalvideo signal input to the pixels, and the pixels perform display.

One subframe period is complete at the same time as the sustain periodis complete. The next subframe period then appears, and once again theaddress period begins. The sustain period again beings after the digitalvideo signal is input to all of the pixels. Note that the order ofappearance of the subframe periods SF1 to SFn is arbitrary.

Similar operations are then repeated in the remaining subframe periods,and display is performed. After completing all of the a subframeperiods, one image is displayed, and one frame period is completed. Whenone frame period is complete, the subframe period of the next frameperiod appears, and the above stated operations are repeated.

The lengths of the address periods Ta1 to Tan of the respective nsubframe periods are each the same in the present invention. Further,the ratio of lengths of the n sustain periods Ts1, . . . , Tsn isexpressed as Ts1: Ts2: Ts3: . . . : Ts(n−1): Tsn=2⁰: 2⁻¹: 2²: . . . :2^(−(n-2)): 2^(−(n-1)).

The gray-scale of each pixel is determined in accordance with duringwhich subframe periods in one frame period the pixel is made to emitlight. For example, when n=8, and taking the brightness of pixels whichemit light in all of the sustain periods as having a value of 100%,pixels which emit light in Ts1 and Ts2 can express a brightness of 75%,and for a case of selecting Ts3, Ts5, and Ts8, a brightness of 16% canbe expressed.

Note that it is possible to freely combine Embodiment 2 with Embodiment1.

Embodiment 3

The electric potential of the opposing electrodes are maintained at thesame electric potential as that of the electric power source potentialduring the address period in Embodiments 1 and 2. Therefore, the ELelements do not emit light. However, the present invention is notlimited to this structure. If an electric potential difference is alwaysformed between the opposing electric potential and the electric powersource potential, on an order at which the EL elements will emit light,when the electric power source potential is applied to the pixelelectrodes, display may also be performed in the address period, similarto the display period.

However, when combining Embodiment 1, in which the EL elements are usedas the light source of the area sensor, with Embodiment 3, it isimportant that the sensor frame period SF be contained within the frameperiod for an area sensor which reads in a single color image.Furthermore, it is important that the three subframe periodscorresponding to RGB be contained in R, G, and B sensor frame periods,respectively, for an area sensor which reads in a color image.

In addition, when combining Embodiment 2, in which an image is displayedin the sensor portion, with Embodiment 3, the entire subframe period inpractice becomes a period for performing display, and therefore thelengths of the subframe periods are set so as to be SF1: SF2: SF3: . . .: SF(n−1): SFn=2⁰: 2⁻¹: 2⁻²: . . . : 2^(−(n-2)): 2^(−(n-1)). An imagehaving a high brightness can be obtained in accordance with the abovestructure when compared with the drive method in which light is notemitted during the address period.

Embodiment 4

An example of a method of driving the switching TFTs 104 and the ELdriving TFTs 105, which control the operation of the EL elements 106shown in FIG. 2, by a method which differs from that of Embodiment 1 isexplained in Embodiment 4. Note that the structure of the sensor portionis the same as that shown by the embodiment mode, and therefore FIG. 1and FIG. 2 may be referenced.

A top view of an area sensor of Embodiment 4 is shown in FIG. 8.Reference numeral 130 denotes a source signal line driving circuit,reference numeral 132 denotes a gate signal line driving circuit, andboth control the driving of the switching TFT 104 and the EL driving TFT105. Further, reference numeral 131 denotes a sensor source signal linedriving circuit, and reference numeral 133 denotes a sensor gate signalline driving circuit, and both control the driving of the reset TFT 110,the buffer TFT 111, and the selection TFT 112. One each of the sourcesignal line driving circuit and the gate signal line driving circuit areformed in Embodiment 4, but the present invention is not limited to thisstructure. Two source signal line driving circuits may also be formed.Further, two gate signal line driving circuits may also be formed.

Note that the source signal line driving circuit 130, the gate signalline driving circuit 132, the sensor source signal line driving circuit131, and the sensor gate signal line driving circuit 133 are referred toas a driving portion throughout this specification.

The source signal line driving circuit 130 has a shift register 130 a, alevel shifter 130 b, and a sampling circuit 130 c. Note that the levelshifter may be used when necessary, and it need not necessarily be used.Further, a structure is used in Embodiment 4 in which the level shifteris formed between the shift register 130 a and the sampling circuit 130c, but the present invention is not limited to this structure. Astructure in which the level shifter 130 b is incorporated within theshift register 130 a may also be used.

A clock signal CLK and a start pulse signal SP are input to the shiftregister 130 a in the source signal line driving circuit 130. A samplingsignal is output from the shift register 130 a in order to sample ananalog signal. The output sampling signal is input to the level shifter130 b, and it electric potential amplitude is increased, and it isoutput.

The sampling signal output from the level shifter 130 b is input to thesampling circuit 130 c. The analog signal input to the sampling circuit130 c is then sampled by the sampling signal, and input to source signallines S1 to Sx.

On the other hand, the gate signal line driving circuit 132 has a shiftregister and a buffer (neither shown in the figure). Further, the gatesignal line driving circuit 132 may also have a level shifter inaddition to the shift register and the buffer, depending upon thecircumstances.

In the gate signal line driving circuit 132, a gate signal is suppliedto the buffer (not shown in the figure) from the shift register (alsonot shown in the figure), and this is supplied to a corresponding gatesignal line. Gate electrodes of the switching TFTs 104 of one lineportion of pixels are connected to the gate signal lines G1 to Gy, andall of the switching TFTs 104 of the one line portion of pixels must beplaced in an ON state simultaneously, and therefore a buffer in which alarge electric current is capable of flowing is used.

Note that the number of source signal line driving circuits and gatesignal line driving circuits, their structure, and their operation arenot limited to the structure shown by Embodiment 4. The area sensor ofthe present invention is capable of using a known source signal linedriving circuit and a known gate signal line driving circuit.

Next, a timing chart for a case of driving the switching TFT 104 and theEL driving TFT 105 of the sensor portion by an analog method is shown inFIG. 9. A period through which all of the pixels of the sensor portiondisplay light is referred to as one frame period F. One line period Ldenotes a period from the selection of one gate signal line until theselection of the next, separate, gate signal line. For the case of thearea sensor shown in FIG. 2, there are y gate signal lines, andtherefore y line periods L1 to Ly are formed within one frame period.

The number of line periods within one frame period increases along withincreasing resolution, and the driving circuits must be driven at a highfrequency.

First, the electric potential of the electric power source supply linesV1 to Vx is maintained at the constant electric power source potential.The opposing electric potential, the electric potential of the opposingelectrodes of the EL elements 106, is also maintained at a constantelectric potential. The electric power source potential has an electricpotential difference with the opposing electric potential on the orderthat the EL elements 106 will emit light when the electric power supplypotential is applied to the pixel electrodes of the EL elements 106.

In the first line period L1, all of the switching TFTs 104 connected tothe gate signal line G1 are placed in an ON state in accordance with agate signal input to the gate signal line G1 from the gate signal linedriving circuit 132. The analog signal is then input to the sourcesignal lines S1 to Sx in order from the source signal line drivingcircuit 130. The analog signal input to the source signal lines S1 to Sxis input to the gate electrodes of the EL driving TFTs 105 through theswitching TFTs 104 which are in an ON state.

The size of the electric current flowing in a channel forming region ofthe EL driving TFTs 105 is controlled by the height of the electricpotential (voltage) of the signal input to the gate electrodes of the ELdriving TFTs 105. Therefore, the electric potential applied to the pixelelectrodes of the EL elements 106 is determined by the height of theelectric potential of the analog signal input to the gate electrodes ofthe EL driving TFTs 105. The EL elements 105 are controlled by theelectric potential of the analog signal, and perform the emission oflight. Note that, in the case of Embodiment 4, the analog signal inputto all of the pixels is maintained at an electric potential having thesame height.

The first line period L1 is complete when input of the analog signal tothe source signal lines S1 to Sx is completed. Note that the perioduntil the input of the analog signal to the source signal lines S1 to Sxis complete may also be combined with a horizontal return period andtaken as one line period. The second line period L2 begins next, and allof the switching TFTs 104 connected to the gate signal line G1 areplaced in an OFF state. All of the switching TFTs 104 connected to thegate signal line G2 are then placed in an ON state in accordance with agate signal input to the gate signal line G2. Then, similar to the firstline period L1, the analog signal is input in order to the source signallines S1 to Sx.

The above operations are repeated up through the gate signal line Gy,and all of the line periods L1 to Ly are complete. When all of the lineperiods L1 to Ly are completed, one frame period is complete. The ELelements of all of the pixels perform light emission by completing oneframe period. Note that all of the line periods L1 to Ly and a verticalreturn period may also be combined and taken as one frame period.

It is necessary for the pixels to emit light in all of the samplingperiods ST1 to STy with the present invention, and for the case of thedriving method of Embodiment 4, it is important that the sensor frameperiod SF is included within the frame period.

Note that an explanation of a method of driving an area sensor forreading in a single color image is explained in Embodiment 4, but a caseof reading in a color image is similar. However, for an area sensorwhich reads in a color image, one frame period is divided into threesubframe periods corresponding to RGB. An analog signal is then input toall of the pixels such that only the EL elements of pixels correspondingto R will emit light in an R subframe period, and only the EL elementsfor the color R perform light emission. The subframe periods for G and Bare similar, and only EL elements of pixels corresponding to therespective color perform light emission.

For the case of an area sensor which reads in a color image, it isimportant that each sustain period of the three subframe periodscorresponding to RGB contain a sensor frame period for R, G, and B (SFr,SFg, SFb), respectively.

Note that if an analog video signal having image information issubstituted for the analog signal for a case of displaying an image inthe sensor portion 101 in the driving method of Embodiment 4, display ofthe image in the sensor portion 101 becomes possible.

Embodiment 5

A cross sectional diagram of an area sensor of the present invention isexplained in Embodiment 5.

FIG. 14B shows a cross sectional diagram of an area sensor of Embodiment5. Reference numeral 301 denotes a switching TFT, reference numeral 302denotes an EL driving TFT, 303 denotes a reset TFT, 304 denotes a bufferTFT, and reference numeral 305 denotes a selection TFT.

Further, reference numeral 242 denotes a p-type semiconductor layer, 248denotes a photoelectric conversion layer, and reference numeral 238denotes a n-type semiconductor layer. A photodiode 306 is formed by thep-type semiconductor layer 242, the photoelectric conversion layer 248,and the n-type semiconductor layer 238. Reference numeral 265 denotes asensor wiring, and the sensor wiring is connected the n-typesemiconductor layer 238 and an external electric power source. Further,the p-type semiconductor layer 242 of the photodiode 306 and the drainregion of the reset TFT 303 is connected each other electrically.

Further, reference numeral 264 denotes a pixel electrode (anode), 266denotes an EL layer and 267 denotes an opposing electrode (cathode). AnEL element 269 is formed by the pixel electrode (anode) 264, the ELlayer 266 and the opposing electrode (cathode) 267. Note that referencenumeral 268 denotes a bank, and that the EL layers 266 of adjacentpixels are separated.

Reference numeral 270 denotes a subject, and light emitted from the ELelement 269 is reflected by the subject 270 and is irradiated to thephotodiode 306. The subject 270 is formed on the side of a sensorsubstrate 200 on which the TFTs are not formed in Embodiment 5.

The switching TFT 301, the buffer TFT 304, and the selection TFT 305 areall n-channel TFTs in Embodiment 5. Further, the EL driving TFT 302 andthe reset TFT 303 are a p-channel TFT. Note that the present inventionis not limited to this structure. Therefore, the switching TFT 301, theEL driving TFT 302, the buffer TFT 304, the selection TFT 305, and thereset TFT 303 may be either n-channel TFTs or p-channel TFTs.

However, when a source region or a drain region of the EL driving TFT302 is electrically connected to the anode 264 of the EL element 269, asin Embodiment 5, it is preferable that the EL driving TFT 302 be ap-channel TFT. Conversely, when the source region or the drain region ofthe EL driving TFT 302 is electrically connected to the cathode of theEL element 269, it is preferable that the EL driving TFT 302 be an-channel TFT.

Note the photodiode and the other TFTs of Embodiment 5 can be formed atthe same time, and therefore the number of process steps can besuppressed.

Note that it is possible to freely combine Embodiment 5 with Embodiments1 to 4.

Embodiment 6

A cross sectional diagram of an area sensor of the present invention,differing from that of Embodiment 5, is explained in Embodiment 6.

FIG. 15 shows a cross sectional diagram of an area sensor of Embodiment6. Reference numeral 701 denotes a switching TFT, reference numeral 702denotes an EL driving TFT, 703 denotes a reset TFT, 704 denotes a bufferTFT, and reference numeral 705 denotes a selection TFT.

Further, reference numeral 738 denotes a n-type semiconductor layer, 748denotes a photoelectric conversion layer, and reference numeral 742denotes a p-type semiconductor layer. A photodiode 706 is formed by then-type semiconductor layer 738, the photoelectric conversion layer 748,and the p-type semiconductor layer 742. Reference numeral 765 denotes asensor wiring, and the sensor wiring electrically connects the p-typesemiconductor layer 742 and an external electric power source. Further,the n-type semiconductor layer 738 of the photodiode 706 and a drainregion of the reset TFT 703 are electrically connected.

Reference numeral 767 denotes a pixel electrode (cathode), 766 denotesan EL layer, and 764 denotes an opposing electrode (anode). An ELelement 769 is formed by the pixel electrode (cathode) 767, the EL layer766, and the opposing electrode (anode) 764. Note that reference numeral768 denotes a bank, and that the EL layers 766 of adjacent pixels areseparated.

Reference numeral 770 denotes a subject, and light emitted from the ELelement 769 is reflected by the subject 770 and is irradiated to thephotodiode 706. Differing from Embodiment 5, the subject 770 is formedon the side of a substrate 700 on which the TFTs are formed inEmbodiment 6.

The switching TFT 701, the EL driving TFT 702, and the reset TFT 703 areall n-channel TFTs in Embodiment 6. Further, the buffer TFT and theselection TFT are p-channel TFTs. Note that the present invention is notlimited to this structure. Therefore, the switching TFT 701, the ELdriving TFT 702, the buffer TFT 704, the selection TFT 705, and thereset TFT 703 may be either n-channel TFTs or p-channel TFTs.

However, when a source region or a drain region of the EL driving TFT702 is electrically connected to the cathode 709 of the EL element 769,as in Embodiment 6, it is preferable that the EL driving TFT 702 be an-channel TFT. Conversely, when the source region or the drain region ofthe EL driving TFT 702 is electrically connected to the anode 712 of theEL element 769, it is preferable that the EL driving TFT 702 be ap-channel TFT.

Furthermore, when the drain region of the reset TFT 703 is electricallyconnected to the p-type semiconductor layer 742 of the photodiode 706,as in Embodiment 6, it is preferable that the reset TFT 703 be an-channel TFT, and that the buffer TFT 704 be a p-channel TFT.Conversely, when the drain region of the reset TFT 703 is electricallyconnected to the p-type semiconductor layer 742 of the photodiode 702,and the sensor wiring 765 is connected to the n-type semiconductor layer738, it is preferable that the reset TFT 703 be a p-channel TFT, andthat the buffer TFT 704 be a n-channel TFT.

Note the photodiode 706 and the other TFTs of Embodiment 6 can be formedat the same time, and therefore the number of process steps can besuppressed.

Note also that it is possible to freely combine Embodiment 6 withEmbodiments 1 to 5.

Embodiment 7

A method of producing a sensor portion of an area sensor of the presentinvention will be described with reference to FIGS. 10A to 14B. Thesensor portion has switching TFTs 301, EL driving TFTs 302, reset TFTs303, buffer TFTs 304, selective TFTs 305, and diodes 306 on the samesubstrate.

First, referring to FIG. 10A, a substrate 200 made of glass such asbarium bolosilicate glass and aluminobolosilicate glass (e.g., #7059glass and #1737 glass produced by Corning) is used in this embodiment.The substrate 200 is not particularly limited as long as it has lighttransparency. A quartz substrate, a glass substrate, a ceramicsubstrate, or the like may be used. Furthermore, a plastic substrate maybe used, which has heat resistance that can withstand a treatmenttemperature in this embodiment.

As the substrate 200, a stainless substrate may be used. However, sincea stainless substrate is not transparent, it is effective only when anEL element 769 emits light upward as shown in FIG. 15.

An insulating film (underlying film) made of silicon oxide is formed onthe substrate 200 so as to cover it. The insulating film can be made ofa silicon oxide film, a silicon nitride film, or a silicon oxide nitridefilm. For example, a silicon oxide nitride film made of SiH₄, NH₃, andN₂O may be formed to a thickness of 250 to 800 nm (preferably, 300 to500 nm) by plasma CVD. Similarly, a hydrogenated silicon oxide nitridefilm made of SiH₄ and N₂O may be formed to a thickness of 250 to 800 nm(preferably, 300 to 500 nm). In this embodiment, an insulating film madeof silicon oxide is formed to a thickness of 250 to 800 nm so as to havea single-layer configuration. A material for the insulating film is notlimited to silicon oxide.

Next, a flattening insulating film 201 is formed by polishing theinsulating film by a CMP method. The CMP method is conducted by a knownmethod. In polishing an oxide film, slurry of a solid-liquid dispersionsystem is generally used, in which an abrasive of 100 to 1000 nmφ isdispersed in an aqueous solution containing a reagent such as a pHregulator. In this embodiment, silica slurry (pH=10 to 11) is used, inwhich 20% by weight of fumed silica particles obtained by thermallydissolving silicon chloride gas in an aqueous solution with potassiumhydroxide added thereto are dispersed.

After the flattening insulating film 201 is formed, semiconductor layers202 to 208 are formed thereon. The semiconductor layers 202 to 208 areobtained by forming a semiconductor film having an amorphous structureby a known method (e.g., sputtering, LPCVD, plasma CVD, or the like),crystallizing the semiconductor film by known crystallization process(e.g., laser crystallization, thermal crystallization, thermalcrystallization using a catalyst such as nickel, or the like) to obtaina crystalline semiconductor film, and patterning the crystallinesemiconductor film to a desired shape. The semiconductor layers 202 to208 are formed to a thickness of 25 to 80 nm (preferably, 30 to 60 nm).Although there is no particular limit to a material for the crystallinesemiconductor film, a silicon or silicon germanium (Si_(x)Ge_(1-x))alloy may be preferably used. In this embodiment, an amorphous siliconfilm of 55 nm is formed by plasma CVD, and thereafter, a solutioncontaining nickel is held onto the amorphous silicon film. After theamorphous silicon film is dehydrogenated at 500° C. for one hour, thefilm is thermally crystallized at 550° C. for four hours. Furthermore,the amorphous silicon film is subjected to laser annealing for thepurpose of enhancing crystallization, whereby a crystalline silicon filmis formed. The crystalline silicon film is patterned by photolithographyto form the semiconductor layers 202 to 208.

After the semiconductor layers 202 to 208 are formed, they may be dopedwith a trace amount of an impurity element (boron or phosphorus) so asto control the threshold values of TFTs.

In the case of producing a crystalline semiconductor film by lasercrystallization, a pulse-oscillation type or continuous light-emittingtype excimer laser, a YAG laser, and a YVO₄ layer can be used. In thecase of using these lasers, a laser beam emitted from a laser oscillatormay be condensed in a line shape by an optical system and radiated to asemiconductor film. Conditions of crystallization are appropriatelyselected by those skilled in the art. However, in the case of using anexcimer laser, a pulse oscillation frequency is set to be several 300Hz, and a laser energy density is set to be 100 to 400 mJ/cm²(typically, 200 to 300 mJ/cm²). Furthermore, in the case of using a YAGlaser, the second harmonic thereof may be used, with a pulse oscillationfrequency set at several 30 to 300 kHz, and a laser energy density setat 300 to 600 mJ/cm² (typically 350 to 500 mJ/cm²). Then, laser beamscondensed in a line shape with a width of 100 to 1000 μm (e.g., 400 μm)may be radiated to the entire surface of a substrate with an overlappedratio of the line-shaped laser beams set at 50% to 98%.

Then, a gate insulating film 209 covering the semiconductor layers 202to 208 is formed. The gate insulating film 209 is formed of aninsulating film containing silicon with a thickness of 40 to 150 nm byplasma CVD or sputtering. In this embodiment, a silicon oxide nitridefilm (composition ratio: Si=32%, O=59%, N=7%, H=2%) is formed to athickness of 110 nm by plasma CVD. Needless to say, the gate insulatingfilm is not limited to a silicon oxide nitride film. Another insulatingfilm containing silicon may be used as a single-layer or multi-layerconfiguration.

In the case of using a silicon oxide film as the insulating film, theinsulating film can be formed by mixing tetraethyl orthosilicate (TEOS)and O₂ by plasma CVD, setting a reaction pressure at 40 Pa and asubstrate temperature at 300° C. to 400° C., and allowing discharge tooccur at a high-frequency (13.56 MHz) power density of 0.5 to 0.8 W/cm².The silicon oxide film thus produced is subjected to thermal annealingat 400° C. to 500° C., thereby exhibiting satisfactory characteristicsas the gate insulating film.

Then, as shown in FIG. 10A, a first conductive film 210 a (thickness: 20to 100 nm) and a second conductive film 210 b (thickness: 100 to 400 nm)are stacked on the gate insulating film 209. In this embodiment, thefirst conductive film 210 a made of a TaN film with a thickness of 30 nmand the second conductive film 210 b made of a W film with a thicknessof 370 nm are stacked. The TaN film is formed by sputtering using Ta asa target in a nitrogen atmosphere. The W film is formed by sputteringusing W as a target. The W film can also be formed by thermal CVD, usingtungsten hexafluoride (WF₆). In any case, the W film needs to have a lowresistance so as to be used as a gate electrode, and the resistance ofthe W film is desirably 20 μΩcm or less. By enlarging crystal particles,the W film is allowed to have a low resistance. However, in the casewhere a number of impurity elements such as oxygen are present in the Wfilm, crystallization of the W film is inhibited to have a highresistance. Thus, in this embodiment, the W film is formed by sputteringusing W with a high purity (99.9999%) as a target in such a manner thatimpurities are not mixed from a vapor phase during film formation,whereby the resistance of 9 to 20 μΩcm of the W film can be realized.

In this embodiment, although the first conductive film 210 a is made ofTaN, and the second conductive film 210 b is made of W, there is noparticular limit to the materials. The first and second conductive films210 a and 210 b may be made of an element selected from Ta, W, Ti, Mo,Al, Cu, Cr, and Nd, or an alloy material or a compound materialcontaining the element as a main component. Furthermore, a semiconductorfilm such as a polycrystalline silicon film doped with an impurityelement such as phosphorus may be used. An AgPdCu alloy may also beused. Furthermore, it may be possible that the first conductive film ismade of a tantalum (Ta) film, and the second conductive film is made ofa W film. It may also be possible that the first conductive film is madeof a titanium nitride (TiN) film, and the second conductive film is madeof a W film. It may also be possible that the first conductive film ismade of tantalum nitride (TaN) film, and the second conductive film ismade of an Al film. It may also be possible that the first conductivefilm is made of a tantalum nitride (TaN) film, and the second conductivefilm is made of a Cu film.

Next, a mask 211 made of a resist is formed by photolithography, andfirst etching process for forming electrodes and wiring is conducted(FIG. 10B). The first etching process is conducted under first andsecond etching conditions. In this embodiment, under the first etchingcondition, an inductively coupled plasma (ICP) etching method is used,CF₄, Cl₂, and O₂ are used as etching gas, a gas flow ratio thereof isset at 25/25/10 (sccm), and a coil-shaped electrode is supplied with anRF (13.56 MHz) power of 500 W under a pressure of 1 Pa to generateplasma, whereby etching is conducted. The substrate side (sample stage)is also supplied with an RF (13.56 MHz) power of 150 W, whereby asubstantially negative self-bias voltage is applied. The W film isetched under the first etching condition, thereby forming taperedportions in a first conductive layer. An etching speed with respect to Wunder the first etching condition is 200.39 nm/min, and an etching speedwith respect to TaN is 80.32 nm/min, and a selection ratio of W withrespect to TaN is about 2.5. Furthermore, the taper angle of W becomesabout 26° under the first etching condition.

In the first etching process, by forming the mask 211 made of a resistin an appropriate shape, the ends of the first conductive layer and thesecond conductive layer are tapered due to the effect of the biasvoltage applied to the substrate side. The angle of the tapered portionmay be 15° to 45°. Thus, first-shaped conductive layers 212 to 216composed of first conductive layers 212 a to 216 a and second conductivelayers 212 b to 216 b are formed by the first etching process. Referencenumeral 217 denotes a gate insulating film, and regions not covered withthe first-shaped conductive layers 212 to 216 are etched by about 20 to50 nm, whereby thin regions are formed.

Then, second etching process is conducted without removing the mask madeof a resist (FIG. 10C). Herein, CF₄, Cl₂, and O₂ are used as etchinggas, a gas flow ratio thereof is set at 25/25/10 (sccm), and acoil-shaped electrode is supplied with an RF (13.56 MHz) power of 500 Wunder a pressure of 1 Pa to generate plasma, whereby etching isconducted. The substrate side (sample stage) is also supplied with an RF(13.56 MHz) power of 20 W, whereby a substantially negative self-biasvoltage is applied. An etching speed with respect to W in the secondetching process is 124.62 nm/min, and an etching speed with respect toTaN is 20.67 nm/min, and a selection ratio of W with respect to TaN isabout 6.05. Thus, the W film is selectively etched. The taper angle of Wobtained by second etching becomes about 70°. During the second etchingprocess, second conductive layers 218 b to 222 b are formed. On theother hand, the first conductive layers 212 a to 216 a are hardly etchedto form first conductive layers 218 a to 222 a. Reference numeral 223denotes a gate insulating film, and regions not covered withsecond-shaped conductive layers 218 to 222 are etched by about 20 to 50nm, whereby thin regions are formed.

An electrode formed of the first conductive layer 218 a and the secondconductive layer 218 b will become an N-channel type buffer TFT 304 inthe late step, and an electrode formed of the first conductive layer 219a and the second conductive layer 219 b will become an N-channel typeselective TFT 305 in the later step. Similarly, an electrode formed ofthe first conductive layer 220 a and the second conductive layer 220 bwill become a P-channel type reset TFT 303 in the later step, anelectrode formed of the first conductive layer 221 a and the secondconductive layer 221 b will become an N-channel type switching TFT 301in the later step, and an electrode formed of the first conductive layer222 a and the second conductive layer 222 b will become a P-channel typeEL driving TFT 302 in the later step.

Then, first doping process is conducted to obtain a state in FIG. 11A.Doping is conducted using the second conductive layers 218 b to 222 b asa mask with respect to an impurity element, in such a manner that theimpurity element is added to the semiconductor layers below the taperportions of the first conductive layers 218 a to 222 a. There is noconductive layer above the semiconductor layers 205 and 206, so thatthese semiconductor layers are doped from above the gate insulating film223. In this embodiment, plasma doping is conducted using phosphorus asan impurity element at a dose amount of 3.5×10¹² and an acceleratingvoltage of 90 keV. Thus, low-concentration impurity regions 224 a to 228a, 229, and 230 not overlapped with the first conductive layers, andlow-concentration impurity regions 224 b to 228 b overlapped with thefirst conductive layers are formed in a self-alignment manner. Theconcentration of phosphorus added to the low-concentration impurityregions 224 b to 228 b is 1×10¹⁷ to 1×10¹⁸ atoms/cm³, and has a gentleconcentration gradient along the thickness of the taper portions of thefirst conductive layers 218 a to 222 a. In the semiconductor layersoverlapped with the taper portions of the first conductive layers 218 ato 222 a, although the impurity concentration is slightly decreased fromthe ends of the taper portions of the first conductive layers 218 a to222 a, the concentration is substantially the same.

A mask 231 made of a resist is formed, and second doping process isconducted, whereby an impurity element providing an N-type to thesemiconductor layers is added (FIG. 11B). Doping may be conducted by iondoping or ion implantation. Ion doping is conducted under the conditionsof a dose amount of 1×10¹³ to 5×10¹ atoms/cm², and an accelerationvoltage of 60 to 100 keV. In this embodiment, doping is conducted at adose amount of 1.5×10¹⁵ atoms/cm² and an acceleration voltage of 80 keV.As an impurity element providing an N-type, an element belonging to theGroup-XV, typically, phosphorus (P) or arsenic (As) is used. Herein,phosphorus (P) is used. In this case, the conductive layers 218 to 222function as a mask with respect to the impurity element providing anN-type, whereby high-concentration impurity regions 232 a to 236 a, 237,and 238, low-concentration impurity regions 232 b to 236 b notoverlapped with the first conductive layers, and low-concentrationimpurity regions 232 c to 236 c overlapped with the first conductivelayers are formed in a self-alignment manner. The high-concentrationimpurity regions 232 a to 236 a, 237, and 238 are supplied with animpurity element providing an N-type in a concentration range of 1×10²⁰to 1×10²¹ atoms/cm³.

It is not required that the semiconductor films to be a P-channel typeare doped with an N-type impurity in the second doping process shown inFIG. 11B. Therefore, the mask 231 may be formed so as to completelycover the semiconductor layers 204, 206, and 208, thereby preventing thesemiconductor layers 204, 206, and 208 from being doped with an N-typeimpurity. Alternatively, the mask 231 is not provided above thesemiconductor layers 204, 206 and 208, and the polarity thereof may bereversed in third doping process.

Then, the mask 231 made of a resist is removed, and a mask 239 made of aresist is newly formed to conduct third doping process. Because of thethird doping process, impurity regions 240 a to 240 c, 241 a to 241 c,and 242 are formed, in which an impurity element providing aconductivity (P-type) opposite to the above-mentioned conductivity(N-type) is added to the semiconductor layers to be active layers ofP-channel type TFTs (FIG. 11C). The first conductive layers 220 b and222 b are used as a mask with respect to an impurity element, and animpurity element providing a P-type is added to form impurity regions ina self-alignment manner. There of no conductive layer above the impurityregion 242, so that the impurity region 242 is doped from above the gateinsulating film 223. In this embodiment, the impurity regions 240 a to240 c, 241 a to 241 c, and 242 are formed by ion doping using diborane(B₂H₆). During the third doping process, the semiconductor layers toform N-channel type TFTs are covered with the mask 239 made of a resist.During the first and second doping process, the impurity regions 240 a,240 b, and 240 c are supplied with phosphorus in differentconcentrations. However, by conducting doping so that the concentrationof the impurity element providing a P-type becomes 2×10²⁰ to 2×10²¹atoms/cm³ in any region, there is no problem for these regions tofunction as source regions and drain regions of P-channel type TFTs.

Then, the impurity element added to the respective semiconductor layersis activated. Activation is conducted by thermal annealing using anannealing furnace. Thermal annealing may be conducted in a nitrogenatmosphere with an oxygen concentration of 1 ppm or less (preferably,0.1 ppm or less) at 400° C. to 700° C. (typically, 500° C. to 550° C.).In this embodiment, activation is conducted by heat treatment at 550° C.for four hours. In addition to thermal annealing, laser annealing orrapid thermal annealing (RTA method) can be applied.

Furthermore, activation may be conducted after forming a firstinterlayer insulating film. In the case where a wiring material used forwiring is weak to heat, it is preferable to conduct activation afterforming an interlayer insulating film (insulating film mainly containingsilicon, e.g., silicon nitride film) in order to protect wiring and thelike, as in this embodiment.

Furthermore, heat treatment is conducted at 300° C. to 550° C. for 1 to12 hours in an atmosphere containing 3% to 100% hydrogen, whereby thesemiconductor layers are hydrogenated. In this embodiment, heattreatment is conducted at 410° C. for one hour in a nitrogen atmospherecontaining about 3% hydrogen. In this step, unpaired connecting ends ofthe semiconductor layers are terminated with thermally excited hydrogen.As another hydrogenation means, there is plasma hydrogenation (usinghydrogen excited with plasma).

Furthermore, hydrogenation may be conducted after a passivation film isformed.

During the above-mentioned steps, impurity regions are formed in therespective semiconductor layers.

Then, the mask 239 made of a resist is removed to conduct third etchingprocess. In this embodiment, using the conductive layers 218 to 222 as amask, the gate insulating film is etched.

Because of the third etching process, gate insulating films 243 c to 247c are formed under the second conductive layers 243 b to 247 b (FIG.12A).

Then, a passivation film 271 is formed so as to cover the substrate 200(FIG. 12B). The passivation film 271 can be made of a silicon oxidefilm, a silicon nitride film, or a silicon oxide nitride film. Forexample, a silicon oxide nitride film made of SiH₄, NH₃, and N₂O may beformed to a thickness of 10 to 800 nm (preferably, 50 to 500 nm) byplasma CVD. Similarly, a hydrogenated silicon oxide nitride film made ofSiH₄ and N₂O may be formed to a thickness of 50 to 800 nm (preferably,10 to 500 nm). In this embodiment, the passivation film made of nitrogenoxide is formed to a thickness of 10 to 800 nm with a single-layerconfiguration.

Then, a mask 272 made of a resist is formed by photolithography, andfourth etching process for forming an amorphous silicon film 248 isconducted. The resist mask 272 is formed so as to cover the substrate,and to come into contact with a part of the P-type semiconductor layer242 and the N-type semiconductor layer 238 (FIG. 12C). Then, only thesilicon nitride film is etched. In this embodiment, ICP etching is used,CF₄, Cl₂, and O₂ are used as etching gas, a gas flow ratio is set at40/60/35 (sccm), and a coil-shaped electrode is supplied with an RF(13.56 MHz) power of 500 W under the pressure of 1 Pa to generateplasma, whereby etching is conducted.

Then, the mask 272 made of a resist is removed. An amorphous siliconfilm 248 is formed between the N-type semiconductor layer 242 and theP-type semiconductor layer 238 so as to come into contact with a part ofthe N-type semiconductor layer 242 and the P-type semiconductor layer238 (FIG. 13A). The semiconductor film having an amorphous structure isformed by a known method (e.g., sputtering, LPCVD, plasma CVD, or thelike). The amorphous silicon film 248 is formed to a thickness,preferably one to ten times that of the N-channel type semiconductorlayer 242 and the P-channel type semiconductor layer 238. In thisembodiment, the amorphous silicon film 248 is formed to a thickness of25 to 800 nm. Although there is no particular limit to a material forthe crystalline semiconductor film, it may be preferably formed ofsilicon or a silicon germanium (Si_(x)Ge_(1-x)) alloy. In thisembodiment, after an amorphous silicon film with a thickness of 55 nm isformed by plasma CVD, a solution containing nickel is held onto theamorphous silicon film.

Then, a first interlayer insulating film 235 is formed (FIG. 13B). Thefirst interlayer insulating film 235 is obtained by forming aninsulating film containing silicon to a thickness of 100 to 200 nm byplasma CVD or sputtering. In this embodiment, a silicon oxide nitridefilm with a thickness of 150 nm is formed by plasma CVD. Needless tosay, the first interlayer insulating film 235 is not limited to asilicon oxide nitride film. Another insulating film containing siliconmay be formed as a single-layer or multi-layer configuration. Then, thefirst interlayer insulating film 249 is patterned so as to form contactholes reaching the impurity regions 232 a, 233 a, 235 a, 238, 240 a, 241a, and 242.

Then, source lines 251 to 256, and drain lines 257 to 262 are formed. Inthis embodiment, as these lines, a film mainly containing Al or Ag, or amaterial having excellent reflectivity such as a layered film thereofare desirably used.

Then, as shown in FIG. 14A, a second interlayer insulating film 249 isformed. By using resin such as polyimide, polyamide, polyimideamide, andacrylic resin, the second interlayer insulating film 249 can have a flatsurface. In this embodiment, a polyimide film with a thickness of 0.7 μmis formed over the entire surface of the substrate as the secondinterlayer insulating film 249.

Next, as shown in FIG. 14B, a bank 268 made of a resin material isformed. The bank 268 may be formed by patterning an acrylic film or apolyimide film with a thickness of 1 to 2 μm. The bank 268 may be formedalong the source line 256 or the gate line (not shown). The bank 268 maybe used as a shielding film by mixing a pigment or the like in the resinmaterial forming the bank 268.

Then, an EL layer 266 is formed. More specifically, an organic ELmaterial to be the EL layer 266 dissolved in a solvent such aschloroform, dichloromethane, xylene, toluene, tetrahydrofuran, and thelike is applied, and thereafter, the solvent is vaporized by heattreatment. Thus, a coating (EL layer) made of an organic EL material isformed.

In this embodiment, only one pixel is shown. However, a light-emittinglayer emitting red light, a light-emitting layer emitting green light,and a light-emitting layer emitting blue light are formed simultaneouslywith the formation of the EL layer. In this embodiment, as thelight-emitting layer emitting red light, cyanopolyphenylenevinylene isformed to a thickness of 50 nm. Similarly, as the light-emitting layeremitting green light, polyphenylenevinylene is formed to a thickness of50 nm, and as the light-emitting layer emitting blue light,polyalkylphenylene is formed to a thickness of 50 nm. Furthermore,1,2-dichloromethane is used as a solvent, and the solvent is vaporizedby heat treatment with a hot plate at 80° C. to 150° C. for 1 to 5minutes.

In this embodiment, although the EL layer has a single-layerconfiguration, a hole injection layer, a hole transport layer, anelectron injection layer, an electron transport layer, and the like maybe additionally provided. Various examples of combinations have alreadybeen reported, and any configuration may be used.

After the EL layer 266 is formed, a positive electrode 267 made of atransparent conductive film is formed to a thickness of 120 nm as acounter electrode. In this embodiment, a transparent conductive film isused, in which 10 to 20% by weight of zinc oxide is added to indiumoxide. The positive electrode 267 is preferably formed by vapordeposition at room temperature so as not to degrade the EL layer 266.

As described above, the buffer TFT 304, the selective TFT 305, the resetTFT 303, the diode 306, the switching TFT 301, the EL driving TFT 302,and the EL element 269 can be formed on the same substrate.

In this embodiment, Embodiments 1 to 5 can be arbitrarily combined.

Embodiment 8

In a method of producing a sensor portion of the area sensor of thepresent invention, a method of producing a photodiode different fromthat in Embodiment 6 will be described with reference to FIG. 16.

FIG. 16 is an enlarged view of a photodiode 306. As shown in FIG. 16, inthe photodiode 306, a metal film 280 is formed on a first interlayerinsulating film 250. The metal film 280 can be formed simultaneouslywith formation of a source line 254 and a drain line 260. As the metalfilm 280, a film mainly containing Al or Ag that is the same material asthat of the lines, or a material having excellent reflectivity such as acompound film thereof is desirably used.

Light is radiated to a subject 270 from an EL element, and lightreflected form the subject 270 is radiated to the photodiode 306.However, in this case, among light passing through the photodiode 306,there exists light that is not radiated to a photoelectric conversionlayer 248. If the metal film 280 is present as shown in FIG. 16, suchlight is reflected from the metal film 280, whereby the photoelectricconversion layer 248 can receive it. Because of this, the photoelectricconversion layer 248 can receive more light.

In this embodiment, Embodiments 1 to 7 can be arbitrarily combined.

Embodiment 9

In this embodiment, an exemplary EL display apparatus (light-emittingapparatus) produced according to the present invention will be describedwith reference to FIGS. 17A-17B and 18A-18C.

FIG. 17A is a top view of a TFT substrate of an EL display apparatus ofthe present invention. In the present specification, the TFT substraterefers to the one on which a pixel portion is provided.

A pixel portion 4002, a source signal line driving circuit 4003 a for asensor, a source signal line driving circuit 4003 b for an EL element, agate signal line driving circuit 4004 a for an EL element, and a gatesignal line driving circuit 4004 b for a sensor are provided on asubstrate 4001. According to the present invention, the number of thesource signal line driving circuits and the gate signal line drivingcircuits are not limited to those shown in FIG. 17A. The number of thesource signal line driving circuits and the gate signal line drivingcircuits can be appropriately set by a designer. In this embodiment,although the source signal line driving circuits and the gate signalline driving circuits are provided on the TFT substrate, the presentinvention is not limited thereto. The source signal line drivingcircuits and the gate signal line driving circuits provided on asubstrate separate from the TFT substrate may be electrically connectedto the pixel portion via FPCs or the like.

Reference numeral 4005 denotes drawing-around wiring connected to apower supply line (not shown) provided in the pixel portion 4002.Reference numeral 4005 also denotes drawing-around wiring for a gateconnected to the gate signal line driving circuit 4004 a for a sensorand the gate signal line driving circuit 4004 b for a gate. Referencenumeral 4005 also denotes drawing-around wiring for a source connectedto the source signal line driving circuit 4003 a for a sensor and thesource signal line driving circuit 4003 b for an EL element.

The drawing-around wiring 4005 for a gate and the drawing-around wiring4005 for a source are connected to an IC and the like provided outsideof the substrate 4001 via the FPCs 4006. The drawing-around wiring 4005is also connected to a power source provided outside of the substrate4001 via the FPCs 4006.

FIG. 17B shows an enlarged view of the drawing-around wiring 4005.Reference numeral 4100 denotes drawing-around wiring for R, 4101 denotesdrawing-around wiring for G, and 4102 denotes drawing-around wiring forB.

FIG. 18A shows a top view of an area sensor formed by sealing the TFTsubstrate shown in FIG. 17A with a sealant. FIG. 18B shows across-sectional view taken along a line A-A′ in FIG. 18A, and FIG. 18Cshows a cross-sectional view taken along a line B-B′ in FIG. 18A. Thesame components as those shown in FIGS. 17A and 17B are denoted with thesame reference numerals as those therein.

A sealant 4009 is provided so as to surround the pixel portion 4002, thesource signal line driving circuit 4003 a for a sensor, the sourcesignal line driving circuit 4003 b for an EL element, the gate signalline driving circuit 4004 a for a sensor, and the gate signal linedriving circuit 4004 b for an EL element formed on the substrate 4001.Furthermore, a sealing member 4008 is provided above the pixel portion4002, the source signal line driving circuit 4003 a for a sensor, thesource signal line driving circuit 4003 b for an EL element, the gatesignal line driving circuit 4004 a for a sensor, and the gate signalline driving circuit 4004 b for an EL element. Thus, the pixel portion4002, the source signal line driving circuit 4003 a for a sensor, thesource signal line driving circuit 4003 b for an EL element, the gatesignal line driving circuit 4004 a for a sensor, and the gate signalline driving circuit 4004 b for an EL element are sealed with thesubstrate 4001, the sealant 4009, and the sealing member 4008, using afiller 4210.

Furthermore, the pixel portion 4002, the source signal line drivingcircuit 4003 a for a sensor, the source signal line driving circuit 4003b for an EL element, the gate signal line driving circuit 4004 a for asensor, and the gate signal line driving circuit 4004 b for an ELelement provided on the substrate 4001 have a plurality of TFTs. FIG.18B typically shows driving TFTs (herein, an N-channel type TFT and aP-channel type TFT are shown) 4201 included in the source signal linedriving circuit 4003, and an EL driving TFT (i.e., TFT for controlling acurrent to an EL element) and a photodiode 4211 included in the pixelportion, formed on a base film 4010.

In this embodiment, as the driving TFT 4201, a P-channel type TFT or anN-channel type TFT produced by a known method is used. As the EL drivingTFT 4202, a P-channel type TFT produced by a known method is used.Furthermore, in the pixel portion 4002, a retention capacitance (notshown) connected to a gate of the EL driving TFT 4202 is provided.

An interlayer insulating film (flattening film) 4301 is formed on thedriving TFT 4201, the EL driving TFT 4202, and the photodiode 4211. Apixel electrode (positive electrode) 4203 electrically connected to adrain of the EL driving TFT 4202 is formed on the interlayer insulatingfilm 4301. As the pixel electrode 4203, a transparent conductive filmwith a large work function is used. As the transparent conductive film,a compound of indium oxide and tin oxide, a compound of indium oxide andzinc oxide, zinc oxide, tin oxide, or indium oxide can be used.Furthermore, gallium may be added to the transparent conductive film.

On the pixel electrode 4203, an insulating film 4302 is formed. Theinsulating film 4302 has an opening in a portion corresponding to thepixel electrode 4203. In this opening, an EL layer 4204 is formed on thepixel electrode 4203. As the EL layer 4204, a known organic EL materialor an inorganic EL material can be used. There are a low-molecular type(monomer type) material and a high-molecular type (polymer type)material as the organic EL material. Either material may be used.

The EL layer 4204 may be formed by a known vapor deposition technique ora coating technique. Furthermore, the EL layer may have a multi-layerconfiguration or a single-layer configuration by arbitrarily combining ahole injection layer, a hole transport layer, a light-emitting layer, anelectron transport layer, or an electron injection layer.

On the EL layer 4204, a negative electrode 4205 made of a conductivefilm (typically, conductive film mainly containing aluminum, copper, orsilver, or a layered film composed of this conductive film and anotherconductive film) having a light shielding property is formed.Furthermore, it is desirable to exclude moisture and oxygen present onan interface between the negative electrode 4205 and the EL layer 4204as much as possible. Thus, it is required to form the EL layer 4204 inan atmosphere of nitrogen or noble gas, and to form the negativeelectrode 4205 without bringing it into contact with oxygen andmoisture. In this embodiment, the above-mentioned film-formation ispossible by using a film-formation apparatus of a multi-chamber system(cluster-tool system). The negative electrode 4205 is supplied with apredetermined voltage.

As described above, an EL element 4303 composed of the pixel electrode(positive electrode) 4203, the EL layer 4204, and the negative electrode4205 is formed. Then, a protective film 4209 is formed on the insulatingfilm 4302 so as to cover the EL element 4303. The protective film 4209is effective for preventing oxygen, moisture, and the like from enteringthe EL element 4303.

Reference numeral 4005 denotes drawing-around wiring connected to apower supply line, which is electrically connected to a source region ofthe EL driving TFT 4202. The drawing-around wiring 4005 extends betweenthe sealant 4009 and the substrate 4001, and is electrically connectedto wiring 4301 of the FPCs via an anisotropic conductive film 4300.

As the sealing member 4008, a glass material, a metal material(typically, a stainless material), a ceramics material, and a plasticmaterial (including a plastic film) can be used. As the plasticmaterial, a fiberglass-reinforced plastic (FRP) plate, a polyvinylfluoride film (PVF), a myler film, a polyester film, or an acrylic resinfilm can be used. Furthermore, a sheet having a configuration in whichan aluminum foil is interposed between a PVF film and a myler film canalso be used.

In the case where light is radiated from an EL element toward a covermember side, the cover member must be transparent. In this case, atransparent material, such as a glass plate, a plastic plate, apolyester film, or an acrylic film, is used for the cover member.

As the filler 4210, UV-curable resin or thermosetting resin, as well asinert gas such as nitrogen and argon, can be used. More specifically,polyvinyl chloride (PVC), acrylic resin, polyimide, epoxy resin, siliconresin, polyvinyl butyral (PVB), or ethylenevinyl acetate (EVA) can beused. In this embodiment, nitrogen is used as the filler.

In order to expose the filler 4210 to a moisture-absorbing material(preferably, barium oxide) or an oxygen-adsorbing material, a concaveportion 4007 is provided on the surface of the sealing member 4008 onthe substrate 4001 side, and a moisture-absorbing material or anoxygen-adsorbing material 4207 is disposed therein. Themoisture-absorbing material or oxygen-adsorbing material 4207 is held inthe concave portion 4007 by a concave portion cover member 4208 so asnot to scatter. The concave portion cover member 4208 has a fine meshshape which transmits air and moisture but does not transmit themoisture-absorbing material or the oxygen-adsorbing material 4207. Byproviding the moisture-absorbing material or the oxygen-adsorbingmaterial 4207, the EL element 4303 can be prevented from being degraded.

As shown in FIG. 18C, a conductive film 4203 a is formed so as to comeinto contact with the drawing-around wiring 4005 a, simultaneously withthe formation of the pixel electrode 4203.

Furthermore, the anisotropic conductive film 4300 contains a conductivefiller 4300 a. By thermally crimping the substrate 4001 onto the FPC4006, the conductive film 4203 a on the substrate 4001 and the wiring4301 for an FPC on the FPC 4006 are electrically connected to each othervia the conductive filler 4300 a.

In this embodiment, Embodiments 1 to 7 can be arbitrarily combined.

Embodiment 10

In this embodiment, the case will be described with reference to FIGS.19A to 19C, in which TFTs and EL elements are sealed onto a substratewith a sealing member, and thereafter, the substrate is replaced. FIGS.19A to 19C are cross-sectional views showing the steps of producing apixel portion.

In FIG. 19A, reference numeral 3101 denotes a substrate (hereinafter,referred to as a “device forming substrate”) on which devices are to beformed. On the substrate 3101, a peeling layer 3102 made of an amorphoussilicon film is formed to a thickness of 100 to 500 nm (300 nm in thisembodiment). In this embodiment, although a glass substrate is used asthe device forming substrate 3101, a quartz substrate, a siliconsubstrate, a metal substrate (SUS substrate), or a ceramic substrate maybe used.

The peeling layer 3102 may be formed by thermal CVD under reducedpressure, plasma CVD, sputtering, or vapor deposition. On the peelinglayer 3102, an insulating film 3103 is made of a silicon oxide filmhaving a thickness of 200 nm. The insulating film 3103 may be formed bythermal CVD under reduced pressure, plasma CVD, sputtering, or vapordeposition.

Furthermore, photodiodes 3104 and EL driving TFTs 3105 are formed on theinsulating film 3103. In this embodiment, although the EL driving TFTs3105 are P-channel type TFTs, the present invention is not limitedthereto. The EL driving TFTs 3105 may be P-channel type TFTs orN-channel type TFTs.

A first interlayer insulating film 3107 is formed on the photodiodes3104 and the EL driving TFTs 3105. The first interlayer insulating film3107 is formed covering the photodiodes 3104 and the EL driving TFTs3105, so as to flatten pixel electrodes 3106 (formed later).

Each pixel electrode 3106 is formed so as to be electrically connectedto a drain region of the EL driving TFT 3105. In this embodiment, thepixel electrode 3106 is obtained by forming a transparent conductivefilm (typically, a compound film of indium oxide and tin oxide) having athickness of 100 nm, followed by patterning. The pixel electrode 3106functions as a positive electrode of an EL element.

After the pixel electrodes 3106 are formed, a second interlayerinsulating film 3114 made of a silicon oxide film with a thickness of300 nm is formed. Openings 3108 are formed in the second interlayerinsulating film 3114, and EL layers 3109 with a thickness of 70 nm and anegative electrode 3110 with a thickness of 300 nm are formed by vapordeposition. In this embodiment, the EL layer 3109 has a configuration inwhich a hole injection layer with a thickness of 20 nm and alight-emitting layer with a thickness of 50 nm are stacked. Needless tosay, another known configuration may be used in which a hole-injectionlayer, a hole transport layer, an electron transport layer, or anelectron injection layer are combined with a light-emitting layer.

As described above, an EL element 3111 composed of the pixel electrode(positive electrode) 3106, the EL layer 3109, and the negative electrode3110 is obtained. In this embodiment, the EL element 3111 functions as alight-emitting element.

Next, a substrate (hereinafter, referred to as a “sealing member”) 3113for fixing the devices is attached to the layered configuration obtainedas described above with a first adhesive 3112. In this embodiment,although an elastic plastic film is used as the scaling member 3113, aglass substrate, a quartz substrate, a plastic substrate, a siliconsubstrate, or a ceramic substrate may be used. As the first adhesive3112, it is required to use a material that can allow the peeling layer3102 to be selectively removed later.

Typically, an insulating film made of resin can be used. In thisembodiment, although polyimide is used, acrylic resin, polyamide, orepoxy resin may be used. If the adhesive 3112 is positioned on a side ofan observer (i.e., on a side of a user of an electrooptical apparatus)seen from the EL elements, a material that transmits light needs to beused.

The first adhesive 3112 can shut off the EL elements from theatmosphere. This can substantially completely suppress the degradationof an organic EL material due to oxidation, and the reliability of theEL elements can be substantially enhanced.

Next, as shown in FIG. 19B, the peeling layer 3102 is removed, wherebythe device forming substrate 3101 and the insulating film 3103 arepeeled off. In this embodiment, peeling is conducted by exposing thepeeling layer 3102 to gas containing halogen fluoride. In thisembodiment, chloride fluoride (CIF₃) is used as halogen fluoride, andnitrogen is used as diluted gas. As the diluted gas, argon, helium, orneon may be used. The flow rate of CIF₃ and nitrogen may be set at 500sccm (8.35×10⁻⁶ m³/s), and a reaction pressure thereof may be set at 1to 10 Torr (1.3×10² to 13×10³ Pa). Furthermore, a treatment temperaturemay be a room temperature (typically, 20° C. to 27° C.).

In the above-mentioned case, although a silicon film is etched, aplastic film, a glass substrate, a polyimide film, and a silicon oxidefilm are not etched. More specifically, the peeling layer 3102 isselectively etched by being exposed of CF₃ gas, and finally removedcompletely. The active layers of the photodiode 3104 and the EL drivingTFT 3105 similarly formed of a silicon film are covered with the firstinterlayer insulating film 3107. Therefore, they are not exposed to CIF₃gas and hence, are not etched.

In the case of this embodiment, the peeling layer 3102 is graduallyetched from exposed ends. When the peeling layer 3102 is removedcompletely, the device forming substrate 3101 and the insulating film3103 are separated. At this time, the TFTs and EL elements formed ofstacked thin films remain on the side of the sealing member 3113.

Herein, the peeling layer 3102 is etched from the ends thereof. When thedevice forming substrate 3101 is increased in size, it takes a longertime for the peeling layer 3102 to be completely removed, which is notpreferable. Thus, the peeling layer 3102 is removed by etching,desirably when the device forming substrate 3101 has a size of 3 inchesor less (preferably, one inch or less), measured from the upper leftcorner to the lower right corner.

In this embodiment, the peeling layer 3102 is removed by etching in anatmosphere of CIF₃ gas. The present invention is not limited thereto. Itmay also be possible that a laser beam is radiated to the peeling layer3102 from the device forming substrate 3101 side to vaporize the peelinglayer 3102, whereby the device forming substrate 3101 is peeled off. Inthis case, it is required to appropriately select the kind of a laserbeam and the material for the device forming substrate 3101 so that alaser beam passes through the device forming substrate 3101. Forexample, when a quartz substrate is used as the device forming substrate3101, a YAG laser (fundamental (1064 nm), second harmonic (532 nm),third harmonic (355 nm), fourth harmonic (266 nm)) or an excimer laser(wavelength: 308 nm) is used to form a line-shaped beam and theline-shaped beam may be allowed to pass through the quartz substrate. Anexcimer laser does not pass through a glass substrate. Therefore, if aglass substrate is used as the device forming substrate 3101, afundamental, a second harmonic, and a third harmonic of the YAG laser(preferably, the second harmonic (wavelength: 532 nm)) is used to form aline-shaped beam, and the line-shaped beam may be allowed to passthrough a glass substrate.

In the case of conducting peeling by using a laser beam, the peelinglayer 3102 that is vaporized with a laser beam to be radiated is used.

In addition to the method of using a laser beam, it may also be possiblethat the device forming substrate 3101 is peeled off by dissolving thepeeling layer 3102 in a solution. In this case, it is preferable to usea solution that allows the peeling layer 3102 to be selectivelydissolved.

When the TFTs and the EL elements are transferred to the sealing member3113, as shown in FIG. 19C, a second adhesive 3114 is formed, and asecond device forming substrate 3115 is attached. As the second adhesive3114, an insulating film made of resin (typically, polyimide, acrylicresin, polyamide, or epoxy resin) may be used. Alternatively, aninorganic insulating film (typically, a silicon oxide film) may be used.In the case where the second adhesive 3114 is positioned on an observerside, seen from the EL elements, a material transmitting light needs tobe used.

As described above, the TFTs and the EL elements are transferred fromthe device forming substrate 3101 to the second device forming substrate3115. Consequently, an EL display apparatus interposed between thesealing member 3113 and the second device forming substrate 3115 can beobtained. If the sealing member 3113 and the second device formingsubstrate 3115 are made of the same material, thermal expansioncoefficients thereof become equal to each other. Therefore, theapparatus becomes unlikely to be influenced by stress distortion due toa change in temperature.

In the EL display apparatus produced in this embodiment, the materialfor the sealing member 3113 and the second device forming substrate 3115can be selected without being influenced by heat resistance during aprocess of TFTs. For example, a plastic substrate can be used as thesealing member 3113 and the second device forming substrate 3115,whereby a flexible EL display apparatus can be created.

This embodiment can be carried out by being arbitrarily combined withany of the configurations shown in Embodiments 1 to 8.

Embodiment 11

In this embodiment, the case will be described in which a DLC film isformed over the entire surface of an EL display apparatus or at ends ofan EL display apparatus.

FIG. 20A is a cross-sectional view of an EL display apparatus in which aDLC film is formed over the entire surface of the apparatus. On asubstrate 3201, a switching TFT 3205, an EL driving TFT 3204, and aphotodiode 3206 are formed. Reference numeral 3203 denotes an ELelement. The EL driving TFT 3204 controls a current flowing through theEL element 3203.

The switching TFT 3205, the EL driving TFT 3204, and the EL element 3203are sealed with a sealing member 3202 and a sealant 3208 so as to beshut off from outside air. Reference numeral 3209 denotes drawing-aroundwiring. The drawing-around wiring 3209 extends between the sealant 3208and the substrate 3201, and is exposed to the outside of the space inwhich the EL element 3203 is sealed.

Reference numeral 3210 denotes a DLC film. The DLC film 3210 covers theentire EL display apparatus, excluding a part of the drawing-aroundwiring 3209 exposed to the outside of the space in which the EL element3203 is sealed.

In this embodiment, a DLC film may be formed by ECR plasma CVD, RFplasma CVD, μ-wave plasma CVD, or sputtering. The DLC film has a Ramanspectrum distribution with an asymmetric peak at about 1550 cm⁻¹ and ashoulder at about 1300 cm⁻¹. The DLC film also exhibits a hardness of 15to 25 GPa, when measured by minute hardness meter. Such a carbon filmprotects the surface of a substrate. In particular, a plastic substrateis likely to be damaged. Therefore, covering the surface of theapparatus with a DLC film as shown in FIG. 20A is effective forpreventing damage.

The DLC film is also effective for preventing oxygen and water fromentering the space in which the EL element 3203 is sealed. Thus, byforming the DLC film 3210 so as to cover the sealant 3208 as in thisembodiment, a material promoting the degradation of an EL layer, such asmoisture and oxygen, from outside can be prevented from entering thespace in which the EL element 3203 is sealed.

When the DLC film 3210 is formed, a part of the drawing-around wiring3209 exposed to the outside of the space in which the EL element 3203 issealed is covered with a resist mask or the like, and the resist mask isremoved after the DLC film 3210 is formed. A part of the drawing-aroundwiring 3209 not covered with the DLC film 3210 is connected to wiring3212 for an FPC provided at an FPC 3211 via an anisotropic conductivefilm 3213.

FIG. 20B is a cross-sectional view of an EL display apparatus in thecase where a DLC film is formed at ends of the EL display apparatus. Ona substrate 3301, a switching TFT 3305, an EL driving TFT 3304, and aphotodiode 3306 are formed. Reference numeral 3303 denotes an ELelement, and the EL driving TFT 3304 controls a current flowing throughan EL element 3303.

The switching TFT 3305, the EL driving TFT 3304, the photodiode 3306,and the EL element 3303 are sealed with a sealing member 3302 and asealant 3308 so as to be shut off from outside air. Reference numeral3309 denotes drawing-around wiring. The drawing-around wiring 3309extends between the sealant 3308 and the substrate 3301, and the ELelement 3303 is exposed to the outside of the space in which the ELelement 3303 is sealed.

Reference numeral 3310 denotes a DLC film. The DLC film 3310 is formedso as to cover a part of the sealing member 3302, a part of thesubstrate 3301, and the sealant 3308, excluding a part of thedrawing-around wiring 3309 exposed to the outside of the space in whichthe EL element 3303 is scaled.

The DLC film 3310 is effective for preventing oxygen and water fromentering the space in which the EL element 3303 is sealed. Thus, byforming the DLC film 3310 so as to cover the sealant 3308 as in thisembodiment, a material promoting the degradation of an EL layer, such asmoisture and oxygen, from outside can be prevented from entering thespace in which the EL element 3303 is sealed.

In an EL display apparatus shown in FIG. 20B, the DLC film 3310 isformed only at ends (portions including the sealant) of the EL displayapparatus. Therefore, it is easy to form the DLC film 3310.

When the DLC film 3310 is formed, a part of the drawing-around wiring3309 exposed to the outside of the space in which the EL element 3303 issealed is covered with a resist mask or the like, and the resist mask isremoved after the DLC film 3310 is formed. A part of the drawing-aroundwiring 3309 not covered with the DLC film 3310 is connected to wiring3312 for an FPC provided at an FPC 3311 via an anisotropic conductivefilm 3313.

This embodiment can be carried out by being arbitrarily combined withany of the configurations shown in Embodiments 1 to 10.

Embodiment 12

As an exemplary area sensor of the present invention, a portable handscanner will be described with reference to FIGS. 21A and 21B.

FIG. 21A shows a portable hand scanner, which is composed of a body 401,a sensor portion 402, an upper cover 403, an external connecting port404, and operation switches 405. FIG. 21B shows a state where the uppercover 403 of the portable hand scanner in FIG. 21A is closed.

The area sensor of the present invention is capable of displaying a readimage on the sensor portion 402. Therefore, even if an electronicdisplay is not separately provided to the area sensor, an image can beconfirmed as soon as it is read.

The area sensor of the present invention is also capable of sending animage signal read by the sensor portion 402 to electronic equipmentconnected to the outer side of the portable hand scanner through theexternal connecting port 404, whereby the image is corrected,synthesized, edited, and the like on software.

This embodiment can be arbitrarily combined with any of Embodiments 1 to11.

Embodiment 13

As an exemplary area sensor of the present invention, a portable handscanner different from that of Embodiment 12 will be described withreference to FIG. 22.

Reference numeral 501 denotes a sensor substrate, 502 denotes a sensorportion, 503 denotes a touch panel, and 504 denotes a touch pen. Thetouch panel 503 has light transparency. Because of this, the touch panel503 can transmit light emitted from the sensor portion 502 and lightincident upon the sensor portion 502, and an image on a subject can beread through the touch panel 503. In the case where an image isdisplayed on the sensor portion 502, an image on the sensor portion 502can be seen through the touch panel 503.

When the touch pen 504 contacts the touch panel 503, information at aposition where the touch pen 504 is in contact with the touch panel 503can be captured in an area sensor as an electric signal. As the touchpanel 503 and the touch pen 504 used in this embodiment, any knownmembers can be used, as long as the touch panel 503 has lighttransparency, and information at a position where the touch pen 504contacts the touch panel 503 can be captured in an area sensor as anelectric signal.

The area sensor of the present invention having the above-mentionedconfiguration is capable of reading an image, displaying the read imageon the sensor portion 502, and writing to the captured image with thetouch pen 504. In the area sensor of the present invention, read of animage, display of an image, write to an image can be all conducted inthe sensor portion 502. Thus, the size of the area sensor can beminimized, and the area sensor is allowed to have various functions.

This embodiment can be arbitrarily combined with any of Embodiments 1 to12.

Embodiment 14

In this embodiment, a configuration of a sensor portion of an areasensor will be described, which is different from that shown in FIG. 1.

FIG. 24 shows a circuit diagram of a sensor portion of an area sensor ofthis embodiment. A sensor portion 1001 is provided with source signallines S₁ to S_(x), power supply lines V₁ to V_(x), gate signal lines G₁to G_(y), reset gate signal lines RG₁ to RG_(y), sensor output lines SS₁to SS_(x), and a sensor power source line VB.

The sensor portion 1001 has a plurality of pixels 1002. Each pixel 1002includes one of the source signal liens S₁ to S_(x), one of power supplylines V₁ to V_(x), one of gate signal lines G₁ to G_(y), one of resetgate signal lines RG₁ to RG_(y), one of sensor output lines SS₁ toSS_(x), and the sensor power source line VB.

The sensor output lines SS₁ to SS_(x) are respectively connected toconstant current power sources 1003_ ₁ to 1003_ _(x) .

The pixel 1002 includes a switching TFT 1004, an EL driving TFT 1005,and an EL element 1006. In FIG. 24, although a capacitor 1007 isprovided in the pixel 1002, the capacitor 1007 may not be provided. Thepixel 1002 further includes a reset TFT 1010, a buffer TFT 1011, aselective TFT 1012, and a photodiode 1013.

The EL element 1006 is composed of a positive electrode, a negativeelectrode, and an EL layer provided between the positive electrode andthe negative electrode. In the case where the positive electrode isconnected to a source region or a drain region of the EL driving TFT1005, the positive electrode functions as a pixel electrode and thenegative electrode functions as a counter electrode. In contrast, in thecase where the negative electrode is connected to a source region or adrain region of the EL driving TFT 1005, the positive electrodefunctions as a counter electrode and the negative electrode functions asa pixel electrode.

A gate electrode of the switching TFT 1004 is connected to the gatesignal line (G₁ to G_(y)). One of a source region and a drain region ofthe switching TFT 1004 is connected to the source signal line (S₁ toS_(x)), and the other is connected to the gate electrode of the ELdriving TFT 1005.

One of the source region and the drain region of the EL driving TFT 1005is connected to the power supply line (V₁ to V_(x)), and the other isconnected to the EL element 1006. The capacitor 1007 is provided so asto be connected to the gate electrode of the EL o10 driving TFT 1005 andthe power supply line (V₁ to V_(x)).

A gate electrode of the reset TFT 1010 is connected to the reset gatesignal line (RG₁ to RG_(x)). A source region of the reset TFT 1010 isconnected to the sensor power source line VB. The sensor power sourceline VB is always kept at a constant electric potential (referencepotential). A drain region of the reset TFT 1010 is connected to thephotodiode 1013 and a gate electrode of the buffer TFT 1011.

Although not shown in the figure, the photodiode 1013 has an N-typesemiconductor layer, a P-type semiconductor layer, and a photoelectricconversion layer provided between the N-type semiconductor layer and theP-type semiconductor layer. The drain region of the reset TFT 1010 isconnected to either the P-type semiconductor layer or the N-typesemiconductor layer of the photodiode 1013.

A drain region of the buffer TFT 1011 is connected to the sensor powersource line VB, and is always kept at a constant reference potential. Asource region of the buffer TFT 1011 is connected to a source region ora drain region of the selective TFT 1012.

A gate electrode of the selective TFT 1012 is connected to the gatesignal line (G₁ to G_(x)). One of a source region and a drain region ofthe selective TFT 1012 is connected to the source region of the bufferTFT 1011 as described above, and the other is connected to the sensoroutput line (SS₁ to SS_(x)). The sensor output line (SS₁ to SS_(x)) isconnected to the constant current power source (103_ ₁ to 103_ _(x) ),and is always supplied with a constant current.

In this embodiment, the polarity of the switching TFT 1004 is the sameas that of the selective TFT 1012. That is, when the switching TFT 1004is an N-channel type TFT, the selective TFT 1012 is also an N-channeltype TFT. When the switching TFT 1004 is a P-channel type TFT, theselective TFT 1012 is also a P-channel type TFT.

Unlike the area sensor shown in FIG. 1, in the sensor portion of thearea sensor of this embodiment, a gate electrode of the switching TFT1004 and a gate electrode of the selective TFT 1012 are both connectedto the gate signal lines (G₁ to G_(x)). Therefore, in the case of thearea sensor of this embodiment, the length of a period during which theEL element 1006 of each pixel emits light is the same as that of asampling period (ST₁ to ST_(N)). Because of the above-mentionedconfiguration, the number of wirings can be decreased in the area sensorof this embodiment, compared with the case shown in FIG. 1.

The area sensor of this embodiment is also capable of displaying animage on the sensor portion 1001.

The configuration of this embodiment can be arbitrarily combined withany of Embodiments 1 to 13.

Embodiment 15

Examples of electronic equipment using an area sensor of the presentinvention include a video camera, a digital still camera, a notebookcomputer, a portable information terminal (mobile computer, mobilephone, portable game machine, electronic book, etc.), and the like.

FIG. 25A shows a video camera, which includes a body 2101, a displayportion 2102, an image receiving portion 2103, an operation key 2104, anexternal connecting port 2105, a shutter 2106 and the like. The areasensor of the present invention can be applied to the display portion2102.

FIG. 25B shows a mobile computer, which includes a body 2301, a displayportion 2302, a switch 2303, operation keys 2304, an infrared port 2305,and the like. The area sensor of the present invention can be applied tothe display portion 2302.

FIG. 25C shows a mobile phone, which includes a body 2701, a housing2702, a display portion 2703, a voice input portion 2704, a voice outputportion 2705, operation keys 2706, an external connecting portion 2707,an antenna 2708, and the like. The area sensor of the present inventioncan be applied to the display portion 2703.

As described above, the application range of the present invention isvery large. Thus, the present invention can be used for electronicequipment in various fields.

This embodiment can be arbitrarily combined with the embodiment, and anyof Embodiments 1 to 14.

According to the present invention, due to the above-mentionedconfiguration, light is radiated uniformly to a subject, so that noinconsistencies in lightness are caused in a read image. Furthermore,unlike a conventional example, it is not required to provide a backlightand a light scattering plate separately from a sensor substrate.Therefore, the mechanical strength of an area sensor is increasedwithout requiring precise adjustment of the position of a backlight, alight scattering plate, a sensor substrate, and a subject. As a result,an area sensor can be made small, thin, and light-weight.

The area sensor of the present invention is also capable of displayingan image on a sensor portion, using EL elements. Therefore, even if anelectronic display is not separately provided to the area sensor, animage read by the sensor portion can be displayed on the sensor portion,and the read image can be confirmed immediately.

Furthermore, in a photodiode used in the present invention, aphotoelectric conversion layer is made of an amorphous silicon film, anN-type semiconductor layer is made of an N-type polycrystalline siliconfilm, and a P-type semiconductor layer is made of a P-typepolycrystalline silicon film. The amorphous silicon film is thicker thanthe polycrystalline silicon film, and the ratio in thicknesstherebetween is preferably (1 to 10):1. Since the amorphous silicon filmis thicker than the polycrystalline silicon film, the photoelectricconversion layer can receive more light. According to the presentinvention, the amorphous silicon film has a light absorptivity higherthan that of the polycrystalline silicon film and the like, so that anamorphous silicon film is used for the photoelectric conversion layer.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

The invention claimed is:
 1. A portable information terminal comprising: a plastic substrate; a first inorganic insulating film over the plastic substrate; a gate insulating film over the first inorganic insulating film; a second inorganic insulating film over the gate insulating film; an organic insulating film over the second inorganic insulating film; a first driver circuit and a second driver circuit over the plastic substrate; and a pixel portion over the plastic substrate, the pixel portion comprising a first pixel and a second pixel, each of the first pixel and the second pixel comprising a first to a fourth transistors and a capacitor, each of the transistors comprising a polycrystalline silicon film over the first inorganic insulating film, and a gate electrode overlapping the polycrystalline silicon film with the gate insulating film therebetween, the first pixel comprising: an EL element comprising: a first electrode; a second electrode; and an EL layer between the first electrode and the second electrode, and a touch panel over the EL element, wherein the second inorganic insulating film covers the gate electrodes of the transistors, wherein the organic insulating film covers the second inorganic insulating film, wherein the first electrode, the EL layer and the second electrode are over the organic insulating film, the first electrode being electrically connected to the one of the source and the drain of the first transistor through an opening in the organic insulating film, wherein the pixel portion is between the first and the second driver circuits when seen in a plan view, wherein a first line electrically connects a gate of the second transistor of the first pixel to the first driver circuit, and wherein a second line electrically connects a gate of one of the first to the fourth transistors of the second pixel to the second driver circuit.
 2. The portable information terminal to claim 1, further comprising a sensor in the second pixel, wherein the one transistor of the first to the fourth transistors of the second pixel belongs to a sensor circuit comprising the sensor, and the second driver circuit is a sensor gate signal line driving circuit.
 3. The portable information terminal according to claim 2, wherein the sensor is a photodiode.
 4. The portable information terminal according to claim 1, further comprising: an FPC fixed to the plastic substrate; and a wiring formed on the flexible substrate, configured to connect an element comprised in the first pixel to the FPC.
 5. The portable information terminal according to claim 1, further comprising an adhesive between the first transistor of the first pixel and the plastic substrate.
 6. A portable information terminal comprising: a plastic substrate; a first inorganic insulating film over the plastic substrate; a gate insulating film over the first inorganic insulating film; a second inorganic insulating film over the gate insulating film; an organic insulating film over the second inorganic insulating film; a first driver circuit and a second driver circuit over the plastic substrate; and a pixel portion over the plastic substrate, the pixel portion comprising a first pixel and a second pixel, each of the first pixel and the second pixel comprising a transistor and a capacitor, the transistor comprising a polycrystalline silicon film over the first inorganic insulating film, and a gate electrode overlapping the polycrystalline silicon film with the gate insulating film therebetween, the first pixel comprising: an EL element comprising: a first electrode; a second electrode; and an EL layer between the first electrode and the second electrode, wherein the second inorganic insulating film covers the gate electrode of the transistor, wherein the organic insulating film covers the second inorganic insulating film, wherein the first electrode, the EL layer and the second electrode are over the organic insulating film, the first electrode being electrically connected to a first line, wherein the pixel portion is between the first and the second driver circuits when seen in a plan view, wherein a second line is directly connected to the gate electrode of the transistor, and wherein the capacitor is directly connected to the first line and the transistor.
 7. The portable information terminal to claim 6, wherein the first line is a power supply line.
 8. The portable information terminal to claim 6, further comprising a sensor in the second pixel, wherein the transistor of the second pixel belongs to a sensor circuit comprising the sensor, and the second driver circuit is a sensor gate signal line driving circuit.
 9. The portable information terminal according to claim 8, wherein the sensor is a photodiode.
 10. The portable information terminal according to claim 6, further comprising: an FPC fixed to the plastic substrate; and a wiring formed on the flexible substrate, configured to connect an element comprised in the first pixel to the FPC.
 11. The portable information terminal according to claim 6, further comprising an adhesive between the transistor of the first pixel and the plastic substrate.
 12. A portable information terminal comprising: a plastic substrate; a first inorganic insulating film over the plastic substrate; a gate insulating film over the first inorganic insulating film; a second inorganic insulating film over the gate insulating film; an organic insulating film over the second inorganic insulating film; a first driver circuit and a second driver circuit over the plastic substrate; and a pixel portion over the plastic substrate, the pixel portion comprising a first pixel and a second pixel, each of the first pixel and the second pixel comprising a first to a third transistors, each of the transistors comprising a polycrystalline silicon film over the first inorganic insulating film, and a gate electrode overlapping the polycrystalline silicon film with the gate insulating film therebetween, the first pixel comprising: an EL element comprising: a first electrode; a second electrode; and an EL layer between the first electrode and the second electrode, and wherein the second inorganic insulating film covers the gate electrodes of the transistors, wherein the organic insulating film covers the second inorganic insulating film, wherein the first electrode, the EL layer and the second electrode are over the organic insulating film, wherein the pixel portion is between the first and the second driver circuits when seen in a plan view, wherein a first line is directly connected to the gate electrode of the first transistor, wherein one of a source electrode and a drain electrode of the first transistor is directly connected to one of a source electrode and a drain electrode of the second transistor, wherein the other of the source electrode and the drain electrode of the first transistor is directly connected to a second line, wherein the gate electrode of the second transistor is directly connected to one of a source electrode and a drain electrode of the third transistor, wherein the gate electrode of the third transistor is directly connected to a third line, and wherein a fourth line is directly connected to the other of the source electrode and the drain electrode of the second transistor and the other of the source electrode and the drain electrode of the third transistor.
 13. The portable information terminal to claim 12, wherein the first line is a gate signal line, and wherein the fourth line is a power supply line.
 14. The portable information terminal to claim 12, further comprising a sensor in the second pixel, wherein one transistor of the first to the third transistors of the second pixel belongs to a sensor circuit comprising the sensor, and the second driver circuit is a sensor gate signal line driving circuit.
 15. The portable information terminal according to claim 14, wherein the sensor is a photodiode.
 16. The portable information terminal according to claim 12, further comprising: an FPC fixed to the plastic substrate; and a wiring formed on the flexible substrate, configured to connect an element comprised in the first pixel to the FPC.
 17. The portable information terminal according to claim 12, further comprising an adhesive between the first transistor of the first pixel and the plastic substrate. 